Inertially operated piezoelectric energy harvesting electronic circuitry

ABSTRACT

A device responsive to an acceleration pulse event, the device including: a piezoelectric device configured to generate a voltage over a duration responsive to one or more acceleration pulse events; an electrical storage device configured to receive a portion of the generated voltage to accumulate a charge; an energy dissipating device coupled to the electrical storage device and configured to dissipate the accumulated charge following the one or more acceleration pulse events and not to substantially dissipate the accumulated charge during the one or more acceleration pulse events; and a voltage limiting device coupled to the electrical storage device and configured to limit the portion of the generated voltage applied to the electrical storage device to a predetermined limit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. application Ser. No.15/414,588 filed on Jan. 24, 2017, which is a continuation in part ofU.S. application Ser. No. 14/589,933 filed on Jan. 5, 2015, which is acontinuation in part of U.S. application Ser. No. 14/225,290, filed onMar. 25, 2014, which is a continuation-in-part application of U.S.application Ser. No. 13/207,355, filed on Aug. 10, 2011, which is acontinuation-in-part application of U.S. application Ser. No. 12/164,096filed on Jun. 29, 2008, which claims the benefit of prior filed U.S.Provisional Application No. 60/958,948 filed on Jul. 10, 2007, thecontents of each of which is incorporated herein by reference.

This application is related to U.S. Patent Application Publication Nos.2008/0129151 filed on Dec. 3, 2007 and 2014-0060366 filed on Mar. 2,2013, the content of each which are also incorporated herein byreference.

GOVERNMENT RIGHTS

This invention was made with Government support under contractW15QKN-16-C-0025 awarded by the United States Army. The Government hascertain rights in the invention.

BACKGROUND 1. Field

The present disclosure relates generally to the electronic circuitry forharvesting electrical energy from piezoelectric elements that aresubjected to short duration impact loading such as during the munitionssetback and set-forward acceleration or target impact events, and moreparticularly to high efficiency electronic circuitry for energyharvesting from such piezoelectric elements for storage in electricalstorage devices such as capacitors or for direct use in devices such ascompact electrical initiation or event sensory indication devices or thelike.

2. Prior Art

Thermal batteries represent a class of reserve batteries that operate athigh temperatures. Unlike liquid reserve batteries, in thermal batteriesthe electrolyte is already in the cells and therefore does not require adistribution mechanism such as spinning. The electrolyte is dry, solidand non-conductive, thereby leaving the battery in a non-operational andinert condition. These batteries incorporate pyrotechnic heat sources tomelt the electrolyte just prior to use in order to make themelectrically conductive and thereby making the battery active. The mostcommon internal pyrotechnic is a blend of Fe and KClO₄. Thermalbatteries utilize a molten salt to serve as the electrolyte uponactivation. The electrolytes are usually mixtures of alkali-halide saltsand are used with the Li(Si)/FeS₂ or Li(Si)/CoS₂ couples. Some batteriesalso employ anodes of Li(Al) in place of the Li(Si) anodes. Insulationand internal heat sinks are used to maintain the electrolyte in itsmolten and conductive condition during the time of use. Reservebatteries are inactive and inert when manufactured and become active andbegin to produce power only when they are activated.

Thermal batteries have long been used in munitions and other similarapplications to provide a relatively large amount of power during arelatively short period of time, mainly during the munitions flight.Thermal batteries have high power density and can provide a large amountof power as long as the electrolyte of the thermal battery stays liquid,thereby conductive. The process of manufacturing thermal batteries ishighly labor intensive and requires relatively expensive facilities.Fabrication usually involves costly batch processes, including pressingelectrodes and electrolytes into rigid wafers, and assembling batteriesby hand. The batteries are encased in a hermetically-sealed metalcontainer that is usually cylindrical in shape. Thermal batteries,however, have the advantage of very long shelf life of up to 20 yearsthat is required for munitions applications.

Thermal batteries generally use some type of igniter to provide acontrolled pyrotechnic reaction to produce output gas, flame or hotparticles to ignite the heating elements of the thermal battery.Currently, the following two distinct classes of igniters are availablefor use in thermal batteries.

The first class of igniters operates based on externally providedelectrical energy. Such externally powered electrical igniters, however,require an onboard source of electrical energy, such as a battery orother electrical power source with related shelf life and/or complexityand volume requirements to operate and initiate the thermal battery.Currently available electric igniters for thermal batteries requireexternal power source and decision circuitry to identify the launchcondition and initiate the pyrotechnic materials, for example by sendingan electrical pulse to generate heat in a resistive wire. The electricigniters are generally smaller than the existing inertial igniters, butthey require some external power source and decision making circuitryfor their operation, which limits their application to larger munitionsand those with multiple power sources.

The second class of igniters, commonly called “inertial igniters”,operate based on the firing acceleration. The inertial igniters do notrequire onboard batteries for their operation and are thereby used oftenin high-G munitions applications such as in non-spinning gun-firedmunitions and mortars. This class of inertial igniters is designed toutilize certain mechanical means to initiate the ignition. Suchmechanical means include, for example, the impact pins to initiate apercussion primer or impact or rubbing acting between one or two partpyrotechnic materials. Such mechanical means have been used and arecommercially available and other miniaturized versions of them are beingdeveloped for thermal battery ignition and the like.

In general, both electrical and inertial igniters, particularly thosethat are designed to operate at relatively low impact levels, have to beprovided with the means for distinguishing events such as accidentaldrops or explosions in their vicinity from the firing accelerationlevels above which they are designed to be activated. This means thatsafety in terms of prevention of accidental ignition is one of the mainconcerns in all igniters.

In recent years, new and improved chemistries and manufacturingprocesses have been developed that promise the development of lower costand higher performance thermal batteries that could be produced invarious shapes and sizes, including their small and miniaturizedversions. However, the existing inertial igniters are relatively largeand not suitable for small and low power thermal batteries, particularlythose that are being developed for use in fuzing and other similarapplications, and electrical igniters require some external power sourceand decision making circuitry for their operation, making themimpractical for use in small and low power thermal battery applications.

In addition, the existing inertial igniters are not capable of allowingdelayed initiation of thermal batteries, i.e., initiation a specified(programmed) and relatively long amount of time after the projectilefiring. Such programmable delay time capability would allow thermalbatteries, particularly those that are used to power guidance andcontrol actuation devices or other similar electrical and electronicdevices onboard gun-fired munitions and mortars to be initiated asignificant amount of time into the flight. In such applications,particularly when electrical actuation devices are used, a significantamount of electrical power is usually required later during the flightto aggressively guide the projectile towards the target. Thus, bydelaying thermal battery initiation to when the power is needed, theperformance of the thermal battery is significantly increased and inmost cases it would also become possible to reduce the overall size ofthe thermal battery and its required thermal insulation.

A review of the aforementioned merits and shortcomings of the currentlyavailable electrical and inertial igniters clearly indicates thatneither one can satisfy the need of many thermal batteries, particularlythe small and miniature thermal batteries and the like, for small sizeigniters that are programmable to provide the desired initiation delaytime and to operate safely by differentiating all-fire and variousno-fire events such as accidental drops and vibration and impact duringtransportation and loading and even nearby explosions.

A review of the aforementioned merits and shortcomings of the currentlyavailable electrical and inertial igniters also clearly indicates theadvantages of electrical initiation in terms of its reliability andsmall size of electrical initiation elements such as electrical matches,the possibility of providing “programmable” decision making circuitryand logic to achieve almost any desired all-fire and no-fireacceleration profiles with the help of an acceleration measuring sensor,and to provide the means to program initiation of the thermal battery orthe like a specified amount of time post firing or certain otherdetected event, but also their main disadvantage in terms of theirrequirement of external batteries (or other power sources) andelectronic and electric circuitry and logic and acceleration sensors forthe detection of the all-fire event. On the other hand, the review alsoindicates the simplicity of the design and operation of inertialigniters in differentiating all-fire conditions from no-fire conditionswithout the use of external acceleration sensors and external powersources.

In many applications, an object is subjected to relatively shortduration shock loading. This is for example the case when an object isimpacted by multiple objects traveling at relatively high speed or if anobject traveling at relatively high speed impacts multiple objects orimpacts multiple barriers that are positioned at relatively closedistances. The latter condition is experienced by munitions impactingmultiple barriers of relatively significant strength that are positionedrelatively close to each other. In such cases, the main shortcoming ofcurrently available sensors, such as different types of availableaccelerometers, is that when such barriers induce relatively large shockloading, then before the vibration and other shock loading induced andgenerally oscillatory outputs from the sensor has been “damped” out, thenext shock loading may occur. As a result, it becomes extremelydifficult, and many cases impossible, to isolate the sensor responsefrom each shock loading event. For example, the munitions may experiencemultiple shock loadings of tens of thousands of G that may last 5-10milliseconds or less and be as little as 5-10 milliseconds or lessapart.

In addition, in many applications, such as in munitions, the munitionsstructure would also exhibit one or more significant mode of vibration,including back and forth stress wave traveling phenomenon, which wouldfurther complicate the aforementioned shock loading event profilemeasurement.

In addition, in most applications, it is highly desirable that sensorsfor detection and measurement of the profile of the aforementionedmultiple shock loading, particularly when such multiple shock loadingsoccur very short times apart, to be very small so that they would notoccupy a considerable volume as well as not to significantly alter thedynamic behavior of the object.

In addition to the above volume requirement and object inertiacharacteristic alteration reasons, it is highly desirable to providesensors for shock loading detection and profile measurement that requireno, or minimal, external electrical energy for their operation.

SUMMARY

A need therefore exists for miniature electrically initiated ignitersfor thermal batteries and the like, particularly for use in gun-firedsmart munitions, mortars, small missiles and the like, that operatewithout external power sources and acceleration sensors and circuitryand incorporate the advantages of both electrical igniters and inertialigniters that are currently available. Such miniature electricallyinitiated igniters are particularly needed for very small, miniature,and low power thermal batteries and other similar applications. Forexample, flexible and conformal thermal batteries for sub-munitionsapplications may occupy volumes as small as 0.006 cubic inches (about100 cubic millimeters). This small thermal battery size is similar involume to the inertial igniters currently available and used in largerthermal batteries.

An objective is to provide a new class of “inertial igniters” thatincorporates electrical initiation of the pyrotechnic materials withoutthe need for external batteries (or other power sources). The disclosedigniters are hereinafter referred to as “electrically initiated inertialigniters”. The disclosed “electrically initiated inertial igniters”utilize the firing acceleration to provide electrical power to theigniter electronics and decision making circuitry, start the initiationtiming when the all-fire condition is detected, and electricallyinitiate the pyrotechnic materials at the specified time into theflight. In addition, electrical initiation of pyrotechnic materials isgenerally more reliable than impact or rubbing type of pyrotechnicinitiation. In addition, electronic circuitry and logic are more readilyconfigured to be programmable to the specified all-fire and no-fireconditions.

The method of providing electrical power includes harvesting electricalenergy from the firing acceleration by, for example, using activematerials such as piezoelectric materials. The method of providingelectrical power also includes activation of certain chemical reservemicro-battery using the aforementioned harvested electrical energy,which would in turn provide additional electrical energy to powerdifferent components of the “electrically initiated inertial igniter”.

The disclosed “electrically initiated inertial igniters” can beminiaturized and produced using mostly available mass fabricationtechniques used in the electronics industry, and should therefore be lowcost and reliable.

To ensure safety and reliability, all inertial igniters, including thedisclosed “electrically initiated inertial igniters” must not initiateduring acceleration events which may occur during manufacture, assembly,handling, transport, accidental drops, etc. Additionally, once under theinfluence of an acceleration profile particular to the firing of theordinance, i.e., an all-fire condition, the igniter must initiate withhigh reliability. In many applications, these two requirements competewith respect to acceleration magnitude, but differ greatly in theirduration. For example:

-   -   An accidental drop may well cause very high acceleration        levels—even in some cases higher than the firing of a shell from        a gun. However, the duration of this accidental acceleration        will be short, thereby subjecting the inertial igniter to        significantly lower resulting impulse levels.    -   It is also conceivable that the igniter will experience        incidental long-duration acceleration and deceleration cycles,        whether accidental or as part of normal handling or vibration        during transportation, during which it must be guarded against        initiation. Again, the impulse input to the igniter will have a        great disparity with that given by the initiation acceleration        profile because the magnitude of the incidental long-duration        acceleration will be quite low.

The need to differentiate accidental and initiation accelerationprofiles by their magnitude as well as duration necessitates theemployment of a safety system which is capable of allowing initiation ofthe igniter only during all-fire acceleration profile conditions areexperienced.

In addition to having a required acceleration time profile which shouldinitiate the igniter, requirements also commonly exist for non-actuationand survivability. For example, the design requirements for actuationfor one application are summarized as:

1. The device must fire when given a [square] pulse acceleration of 900G±150 G for 15 ms in the setback direction.

2. The device must not fire when given a [square] pulse acceleration of2000 G for 0.5 ms in any direction.

3. The device must not actuate when given a ½-sine pulse acceleration of490 G (peak) with a maximum duration of 4 ms.

4. The device must be able to survive an acceleration of 16,000 G, andpreferably be able to survive an acceleration of 50,000 G.

The electrical and electronic components of the disclosed electricallyinitiated inertial igniters are preferably fabricated on a singleplatform (“chip”), and are integrated into either the cap or interiorcompartment of thermal batteries or the like, in either case preferablyin a hermetically sealed environment. The disclosed electricallyinitiated inertial igniters should therefore be capable of readilysatisfying most munitions requirement of 20-year shelf life andoperation over the military temperature range of −65 to 165 degrees F.,while withstanding high G firing accelerations.

Some of the features of the disclosed “electrically initiated inertialigniters” for thermal batteries for gun-fired projectiles, mortars,sub-munitions, small rockets and the like include:

-   -   1. The disclosed (miniature) electrically initiated inertial        igniters are capable of being readily “programmed” to almost any        no-fire and all-fire requirements or multiple predefined setback        environments. For these reasons, the disclosed miniature        electrically initiated inertial igniters are ideal for almost        any thermal battery applications, including conformal small and        low power thermal batteries for fuzing and other similar        munitions applications.    -   2. The disclosed (miniature) electrically initiated inertial        igniters can be fabricated entirely on a chip using existing        mass fabrication technologies, thereby making them highly cost        effective and very small in size and volume.    -   3. The disclosed (miniature) electrically initiated inertial        igniters do not require any external power sources for their        operation.    -   4. In those applications in which the thermal battery power is        needed for guidance and control close to the target, the        disclosed (miniature) electrically initiated igniters can be        programmed to initiate ignition long after firing, thereby        eliminating the effects of thermal battery cooling.    -   5. The disclosed (miniature) electrically initiated inertial        igniters are solid-state in design. Their final total volume is        therefore expected to be significantly less than those of        currently available electrical and inertial igniters.    -   6. The disclosed (miniature) electrically initiated inertial        igniter is capable of electric initiation of Zr/BaCrO4 heat        paper mixtures or their equivalents as is currently practiced in        thermal batteries.    -   7. The disclosed (miniature) electrically initiated inertial        igniters are readily packaged in sealed housings using commonly        used mass-manufacturing techniques. As a result, safety and        shelf life of the igniter, thermal battery and the projectile is        significantly increased.    -   8. The solid-state and sealed design of the disclosed        (miniature) electrically initiated inertial igniters should        easily provide a shelf life of over 20 years and capability to        operate within the military temperature range of −65 to 165        degrees F.    -   9. The disclosed (miniature) electrically initiated inertial        igniters can be designed to withstand very high-G firing        accelerations in excess of 50,000 Gs.    -   10. The disclosed (miniature) electrically initiated inertial        igniters are programmable for any no-fire and all-fire        requirements and delayed initiation time following an all-fire        event. The disclosed igniters could therefore be used with other        electrically activated igniters for thermal batteries, munitions        or other similar applications.    -   11. The disclosed (miniature) electrically initiated inertial        igniters can be designed to conform to any geometrical shape of        the available space and thermal batteries.

Accordingly, an electrically initiated inertial igniter for a munitionis provided. The electrically initiated inertial igniter comprising: anelectrical energy generating device configured to generate a voltageover a duration responsive to an acceleration of the munition; a firstelectrical storage device connected to the electrical energy generatingdevice through a voltage divide circuit to receive a portion of thevoltage over the duration; a second electrical storage device connectedto the electrical energy generating device to accumulate the voltage;and a circuit powered by a connection to the electrical energygenerating device, the circuit configured to determine an all-firecondition based on both a connection to the first electrical storagedevice that receives the portion of the voltage and the duration ofvoltage generation and a predetermined accumulated voltage of the secondelectrical storage device.

The electrical energy generating device can be a piezoelectricgenerator.

The electrically initiated inertial igniter can further comprise aresistor connected to the first electrical storage device to drain acharge accumulated in the first electrical storage device resulting fromnon-firing events.

The circuit can comprise: a reset circuit; and a comparator comprising:a first input connected to the first electrical storage, a second inputconnected to a reference voltage, a third input connected to the resetcircuit, and an output that produces an indication of the all-firecondition in response to the predetermined accumulated voltage in theelectrical storage device, wherein the reset circuit is configured toreset the indication when the electrical energy generating device beginsto generate a voltage.

Also provided is a method for electrically initiating an inertialigniter for a munition. The method comprising acts of: providing anelectrical energy generating device to generate a voltage over aduration responsive to an acceleration of the munition; providing afirst electrical storage device connected to the electrical energygenerating device through a voltage divide circuit to receive a portionof the voltage over the duration; providing a second electrical storagedevice connected to the electrical energy generating device toaccumulate the voltage; and providing a circuit powered by a connectionto the electrical energy generating device, the circuit determining anall-fire condition based on both a connection to the first electricalstorage device that receives the portion of the voltage and the durationof voltage generation and a predetermined accumulated voltage of thesecond electrical storage device.

In addition, in certain applications, the electrical energy that isgenerated by the electrical energy generating element, for example thepiezoelectric element, of the device may be desired to be partially orcompletely stored in an electrical energy storage device such as acapacitor for later use by the system electronics or the like, such asfor powering a timing and/or sensory circuitry for initiation of athermal battery after a prescribed amount of time has elapsed and/orafter a certain event has been detected. In such applications, it ishighly desirable for the electrical energy being harvested from theelectrical energy generating element to be highly efficient to make itpossible to minimize the size of the energy harvesting device and itscomponents.

It will also be appreciated by those skilled in the art that whenharvesting electrical energy from shock loading such as thoseexperienced by gun firing or impact or other similar very short duration“pulsed” loading events, the mechanical to electrical energy convertingelements such as piezoelectric elements or magnet and coil elements usedfor this purpose are subjected to very short duration “pulsed”excitation. Currently used electrical energy collection and capacitorstorage methods are, however, extremely inefficient when the “pulse”duration is very short and sometimes in the order of micro-seconds.Methods and means are highly desirable to be developed for efficientharvesting of generated electrical energy that is generated byelectrical energy generators such as piezoelectric elements or magnetand coil elements in the form of very short duration “pulses”.

Accordingly, methods and devices are provided for highly efficientharvesting (collecting) of electrical energy from electrical energygenerators such as piezoelectric elements or magnet and coil elementswhen the generated electrical energy is in the form of very shortduration pulses such as those encountered as a result of gun firing(particularly in small and medium caliber rounds) and upon target impactor the like or in devices specifically designed to subject theelectrical energy generators to intermittent short duration pulses.

There is also a need for methods of designing miniature sensors andtheir electronics for use in objects, such as munitions, for detectingshock loading and measuring the shock loading profile in general andwhen the object is subjected to multiple shock loadings that areexperienced very short times apart. In particular, there is a need formethods to design and fabricate miniature sensors and their electronicsfor munitions to detect multiple shock loading due to impact withsignificant barriers that are relatively close to each other and tomeasure the shock loading profile. Such sensory systems (sensor and itselectronics) must be capable of isolating the sensor response from eachshock loading event, noting that munitions may experience multipleimpact induced shock loadings that are of tens of thousands of G inmagnitude that may last 5-10 milliseconds or less and be as little as5-10 milliseconds or less apart.

There is also a need for miniature sensors for use in objects such asmunitions for detecting shock loading and measuring the shock loadingprofile in general and when the object is subjected to multiple shockloadings that are experienced very short times apart. In munitions, suchshock loadings may be due to firing setback, expulsion of sub-munitions,firing of range extension rockets, or the like, or due to munitionsimpact with significant barriers and/or target objects or the like.

In addition, since in most applications, such as in munitions, thestructure of the munitions would exhibit one or more significant modesof vibration, including back and forth stress wave traveling phenomenon,a need exists for methods to design sensors and their electronics andsuch sensors and their electronics that are capable of isolating themultiple shock loading events being detected and measured to ensuremeasurement of each individual shock loading profile with appropriatelevel of precision.

In addition, a need also exists for methods to design sensors and theirelectronics and such sensors and their electronics for detection andmeasurement of the profile of the aforementioned multiple and shockloading, particularly when such multiple shock loadings occur very shorttime apart to be very small so that they would not occupy a considerablevolume as well as not to significantly alter the dynamic behavior of theobject.

There is also a need for methods to design sensors and their electronicsand such sensors and their electronics for detection and measurement ofthe profile of the aforementioned multiple and shock loadings thatrequire no or minimal external electrical energy for their operation.

Accordingly, methods and devices are provided for miniature sensors andtheir electronics for multiple shock detection and measurement where theshock loading events that are large in amplitude and relatively veryshort in duration and occurs with minimal time separation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the apparatus ofthe present invention will become better understood with regard to thefollowing description, appended claims, and accompanying drawings where:

FIG. 1 illustrates the block diagram of the first class of the disclosedpiezoelectric element based class of programmable electrically initiatedinertial igniter embodiments.

FIG. 2 illustrates the piezoelectric powered programmable eventdetection and logic circuitry for differentiating all no-fire eventsfrom all-fire events and to initiate igniter only when all-fire event isdetected.

FIG. 3 illustrates a comparison of an accidental drop from the firingacceleration induced voltages.

FIG. 4 illustrates an alternative piezoelectric powered programmableevent detection and logic circuitry for differentiating all no-fireevents from all-fire events and to initiate igniter with a programmedtime delay following all-fire event detection.

FIG. 5 illustrates an alternative piezoelectric powered programmableevent detection and logic circuitry for differentiating all no-fireevents from all-fire events and to initiate igniter with a programmedtime delay for medium caliber rounds and the like.

FIG. 6 illustrates a piezoelectric powered programmable event detectionand logic circuitry design for event detection and initiation foroperation over time periods ranging from minutes to days.

FIG. 7 illustrates the block diagram of the second class of thedisclosed piezoelectric element based programmable electricallyinitiated inertial igniter embodiments employing reserve electricallyactivated micro-batteries for pyrotechnic initiation.

FIG. 8 illustrates an alternative piezoelectric powered programmableevent detection and logic circuitry for differentiating all no-fireevents from all-fire events and to initiate igniter following all-fireevent detection.

FIG. 9 illustrates the initiator circuitry portion of the piezoelectricelement based class of programmable electrically initiated inertialigniter embodiments as modified to provide for detection of the thermalbattery or the like activation status.

FIG. 10 illustrates the initiator circuitry portion of the piezoelectricelement based class of programmable electrically initiated inertialigniter embodiments using at least two initiators to increase thermalbattery or the like activation reliability.

FIG. 11 illustrates the initiator circuitry portion of the piezoelectricelement based class of programmable electrically initiated inertialigniter embodiments using at least two initiators with independentcircuitry to further increase thermal battery or the like activationreliability.

FIG. 12 illustrates a permanent magnet and coil type electrical powergenerator alternative to the piezoelectric element based power sourceused in the class of programmable electrically initiated inertialigniter embodiments of FIGS. 1-2 and 4-8.

FIG. 13 illustrates an alternative embodiment of the programmable safetyand all-fire detection circuitry.

FIG. 14 illustrates the method of using the safety and all-firedetection circuitry of embodiment of FIG. 13 to design passiveinitiators for pyrotechnic material or the like.

FIG. 15 illustrates the first embodiment of the passive initiators forpyrotechnic material or the like that is particularly suitable formunitions and other similar applications.

FIG. 16 illustrates the second embodiment of the passive initiators forpyrotechnic material or the like that is particularly suitable formunitions and other similar applications.

FIG. 17 illustrates the basic method for the design of a passiveall-fire setback acceleration (shock) level detection sensor designedwith the safety and all-fire detection circuitry of the embodiment ofFIG. 13.

FIG. 18 illustrates an embodiment of the passive all-fire setbackacceleration (shock) level detection sensor of FIG. 17 as implementedwith Schmitt triggers suitable for use in munitions or other similarapplications with environmental noise and/or high shock levelfluctuations.

FIG. 19 illustrates an alternative embodiment of the programmable safetyand all-fire detection circuitry of the embodiment of FIG. 13.

FIG. 19A illustrates an alternative embodiment of the programmablesafety and all-fire detection circuitry of the embodiment of FIG. 19.

FIG. 20 illustrates an embodiment of the “impact detection and timehistory sensor” used to detect and “record” the numbers and levels ofimpacts that are encountered by munitions or the like over a period oftime.

FIG. 21 illustrates an embodiment of the implementation of the “impactdetection and time history sensor” of FIG. 20.

FIG. 22 is a plot of the “impact detection and time history sensor” ofthe embodiment of FIG. 20 “recording” of the encounter of the munitionsusing the sensor with two significant barriers.

FIG. 23 illustrates another embodiment of the implementation of the“impact detection and time history sensor” of FIG. 20.

FIG. 24 is the schematic of the embodiment of a piezoelectric-basedpowering source for use in the embodiments of FIGS. 13-21 and 23.

FIG. 25A illustrates a model of a piezoelectric element used in thedisclosed embodiments for generating electrical charges for harvestingand sensing when subjected to external loading.

FIG. 25B is a plot of the generated piezoelectric charge as a functiontime during a typical short duration impact (pulsed) loading.

FIG. 26 illustrates circuitry of an embodiment for high efficiencyharvesting of electrical energy generated by piezoelectric or magnet andcoil elements of a generator device when subjected to very shortduration pulses.

FIG. 27 illustrates the one sub-circuitry of the basic circuitry of theembodiment of FIG. 26 for high efficiency harvesting of electricalenergy from piezoelectric elements subjected to very short durationpulses.

FIG. 28 illustrates the plot of typical currents i1, i2 and i3 shown inFIG. 27 generated during short duration loading of the piezoelectricelement of FIG. 26.

FIG. 29 illustrates the plot of typical voltages corresponding profilesof the voltage V_(p) for the open circuit case of the piezoelectricelement as shown in its equivalent circuit of FIG. 25A (dashed line) andin circuit (FIG. 27) voltage during the short duration impact loading ofthe piezoelectric element (solid line).

FIG. 30 illustrates circuitry of another piezoelectric-based energyharvesting embodiment for harvesting electrical energy when the devicepiezoelectric element is subjected to high compressive loads that couldcause its structural failure.

FIG. 31 is the plot of the generated piezoelectric charge profile as afunction time during a typical rapid compressive loading of thepiezoelectric element up to its structural failure.

FIG. 32 illustrates an equivalent circuitry of the circuitry of FIG. 30that is valid during rapid compressive loading of the piezoelectricelement prior its structural failure.

FIG. 33 illustrates the equivalent circuitry of the device of FIG. 30after the piezoelectric element of the device has structurally failed.

FIG. 34 is a typical plot of the generated currents in the circuitry ofthe piezoelectric-based energy harvesting device of FIG. 30 whensubjected to a rapidly increasing compressive load until its structuralfailure.

FIG. 35 is a typical plot of the generated voltages in the circuitry ofthe piezoelectric-based energy harvesting device of FIG. 30 whensubjected to a rapidly increasing compressive load until its structuralfailure.

FIG. 36 illustrates a schematic of the packaging of the piezoelectricelement of a typical shock loading detection and measurement.

FIG. 37 illustrates a plot of a typical short duration shock loading asa function of time that may be experienced by munitions and to bedetected and measured by the provided sensory system.

FIG. 38 illustrates circuitry of a first embodiment of the piezoelectricbased multiple shock loading detection and shock load profile measuringsensor.

FIG. 39 illustrates circuitry of a second embodiment of thepiezoelectric based multiple shock loading detection and shock loadprofile measuring sensor.

FIG. 40 illustrates circuitry of a third embodiment of the piezoelectricbased multiple shock loading detection and shock load profile measuringsensor.

FIG. 41 illustrates a general circuitry of a fourth embodiment of thepiezoelectric based multiple shock loading detection and shock loadprofile measuring sensor.

FIG. 42 illustrates one implementation of the general circuitry of thefourth embodiment of the piezoelectric based multiple shock loadingdetection and shock load profile measuring sensor shown in FIG. 41.

FIG. 43 illustrates another implementation of the general circuitry ofthe fourth embodiment of the piezoelectric based multiple shock loadingdetection and shock load profile measuring sensor shown in FIG. 41.

FIG. 44 illustrates an example of providing a vibration isolation layerto prevent high frequency platform vibration from being transmitted tothe piezoelectric element of a typical piezoelectric based multipleshock loading detection and shock load profile measuring sensor.

FIG. 45 illustrates an example of the implementation of the method ofadding at least one piezoelectric element to actively isolate thepiezoelectric element of the present embodiments of the multiple shockloading detection and shock load profile measuring sensors.

FIG. 46 illustrates the schematic of a typical active isolationcircuitry for driving the added at least one piezoelectric element forvibration isolation and dissipating remaining electrical and mechanicalenergy of the multiple shock loading detection and shock load profilemeasuring sensor.

FIG. 47 illustrates a typical piezoelectric-based electrical energygenerator component of a self-powered device that is intended togenerate electrical energy when subjected to an acceleration pulse.

FIG. 48 illustrates plots of the profiles of typical generatedpiezoelectric charges as a function time during a typical short durationacceleration pulse loading.

FIG. 49 illustrates an alternative embodiment of the acceleration pulseevent detector circuit (programmable safety and all-fire detectioncircuitry) of FIG. 13.

FIG. 50 illustrates an alternative embodiment of the passiveprogrammable electrical initiator of the embodiment of FIG. 15 forpyrotechnic material or the like that is particularly suitable formunitions and other similar applications.

FIG. 51 is the plot of the threshold indicating capacitor chargingvoltage without the voltage limiting Zener diode.

FIG. 52 is the plot of the threshold indicating capacitor chargingvoltage with the voltage limiting Zener diode.

FIG. 53 illustrates the schematic of the first laser activatedinitiation device embodiment.

FIG. 54 illustrates the schematic of the second laser activatedinitiation device embodiment.

FIG. 55 illustrates the schematic of the third laser activatedinitiation device embodiment.

FIG. 56 illustrates the schematic of the fourth laser activatedinitiation device embodiment.

FIG. 57 illustrates the schematic of the fifth laser activatedinitiation device embodiment.

FIG. 58 illustrates the schematic of the sixth laser activatedinitiation device embodiment.

FIG. 59 illustrates the schematic of the seventh laser activatedinitiation device embodiment.

FIG. 60 illustrates the schematic of the eighth laser activatedinitiation device embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The block diagram of a first embodiment of a programmable electricallyinitiated inertial igniter is shown in FIG. 1. In this embodiment, anappropriately sized piezoelectric element (different options of whichare described later in this disclosure) is used, which responds to theaxial accelerations and/or decelerations of the munitions or the like,to which it is affixed via a thermal battery or the like. In response tothe aforementioned axial accelerations and/or decelerations of thepiezoelectric element, a charge is generated on the piezoelectricelement due to the resulting forces acting on the piezoelectric elementdue to its mass and the mass of other elements acting on thepiezoelectric element (if any). As a result, the sign of thecorresponding voltage on the piezoelectric element would readilyindicate the direction of the axial acceleration that is applied to themunitions due to the firing or accidental dropping or other similarno-fire conditions.

However, the detection of the generated piezoelectric element voltagelevels alone is not enough to ensure safety by distinguishing betweenno-fire and all-fire conditions. This is the case since in certainaccidental events such as direct dropping of the igniter, thermalbattery and/or the munitions, the acceleration levels that areexperienced by the igniter may be well above that of the specifiedall-fire acceleration level requirements. For example, when an igniteris dropped over a hard surface, it might experience acceleration levelsof up to 2000 Gs for an average duration of up to 0.5 msec. However, theall-fire acceleration level may be significantly lower, for examplearound 500 Gs, with the difference being in its duration, which may bearound 8-15 msec.

In addition, it is desired to harvest the electrical energy generated bythe piezoelectric elements and store the electrical energy in a storagedevice such as a capacitor to power the igniter electronics circuitryand logics and to initiate the electrical ignition element when all-fireconditions are detected. Then if the voltage of the storage device suchas the capacitor is to be monitored for the detection of the all-fireconditions, then very long term vibration type oscillatory accelerationsand decelerations of relatively low levels which may be experiencedduring transportation or the like may also bring the voltage of thestorage capacitor to the level corresponding to the all-fire levels. Itis therefore evident that the voltage levels generated by activeelements such as piezoelectric elements alone, or total accumulatedenergy cannot be used to differentiate no-fire conditions from all-fireconditions in all munitions since it may have been generated overrelatively long periods of time due to vibration or other oscillatorymotions of the device during transportation or the like.

Thus, to achieve one single electrically initiated inertial igniterdesign that could work for different types of munitions and the like,the igniter has to be capable of differentiating no-fire high-G but lowduration acceleration profiles from those of all-fire and significantlylonger duration acceleration profiles. The device must alsodifferentiate between low amplitude and long term acceleration profilesdue to vibration and all-fire acceleration profiles.

Obviously, if in certain munitions the all-fire acceleration levels weresignificantly higher than the no-fire acceleration levels, then theaforementioned voltage levels of the piezoelectric element used in anigniter device could be used as a threshold to activate the heatingelement (wire electrode) to initiate the pyrotechnic material orinitiate the initiation “delay timing clock”. However, since theall-fire acceleration levels are lower than the no-fire accelerationlevels in some munitions, therefore to achieve one single electricallyinitiated inertial igniter design that could work for all differenttypes of munitions; the igniter has to be capable of differentiating thetwo events based on the duration of the experienced accelerationprofile. In any case, the igniter device must still differentiate longterm low acceleration vibration profiles from those of all-fireacceleration profiles.

The block diagram of FIG. 1 shows the general schematics of anembodiment of an electrically initiated inertial igniter. In the igniterof FIG. 1, at least one piezoelectric element is used to generate acharge (electrical energy) in response to the acceleration and/ordeceleration profile that it experiences due to all no-fire and all-fireevents. The charge generated by the piezoelectric element is then usedto power the detection and safety electronics and logic circuitry andthe detonation capacitor and its activation circuitry, as describedlater in this disclosure. In one embodiment, the electrical energy fromthe piezoelectric element is stored in a separate and relatively smallcapacitor that would act as a controlled power source to power the logiccircuit. This power, supplied by the charged capacitor, would be used toactivate the monitoring circuit logic to provide functionality, allowingfor a range of triggering events to be detected from the piezoelectricelement that are not directly coupled to peak voltage or energydetection of the piezoelectric element. In this way, circuits can bedesigned as described below to prevent detection of momentary spikevoltage that could be accidentally generated by random vibrations oraccidental droppings or other similar accidental events, indicating afalse ignition condition.

The design of the electronics of a programmable electrically initiatedinertial igniter is intended to address the following two basicrequirements. The first requirement is to ensure safety and reliabilityof the thermal battery which must not be initiated during accidentaldrops, transportation vibration, manufacturing or other handling,miss-fire conditions and the like. The second requirement, which isachievable in a miniature igniter only with electronics circuitry, isrelated to one of the key benefits added by electrically operatedignition systems, i.e., the control of the time of battery initiation,which would allow munitions design engineer to have better control overthe power budget and the mission profile of the guided rounds.Furthermore, by having the ability to initiate thermal battery at anypoint of time during the flight of a round allows munitions designer tooptimize the size and efficiency of the thermal battery by operating itat optimum temperature and thereby reduce its required size.

The following two basic and general event detection, safety and ignitionelectronics and logic circuitry options may be used in the variousembodiments disclosed herein. It is, however, appreciated by thoseskilled in the relevant art that other variations of the presentdetection and logic circuitry may also be constructed to perform thedesired functions, which are intended to be within the scope and spiritof the present disclosure.

FIG. 2 shows the basic diagram of one possible design of the electronicscircuitry for use in a piezoelectric element powered electricallyinitiated inertial igniter. The circuitry shown in FIG. 2 is notdesigned to provide a programmable initiation time delay. This featureis shown in a subsequent embodiment described below. The circuitryfunctions as a reusable power source based on harvesting energy from theat least one piezoelectric element and storing the harvested energy inthe capacitor C1. A dedicated safety feature function (SafetyProgramming Feature) detects accidental drop or other accidentalvibration or impact and determines when it is safe to initiate thebattery. A third dedicated function (Initiation Trigger Mode) operatesthe initiation device which starts the battery initiation process, i.e.,to ignite the igniter pyrotechnic material. The circuit incorporatescircuitry to compare thresholds of energy generated by events andcompares these thresholds with appropriately selected reference voltagesat IC1 and IC2 to operate logic that drives the output switching stagesT1 and T2.

The circuitry in FIG. 2 receives energy from at least one piezoelectricelement that converts mechanical energy harvested from the firingacceleration into electrical charge. Diode bridge B1, rectifies thisenergy and dumps it into the capacitor C1 which is sufficiently large toserve as a power supply to the rest of the circuitry. The diode bridgeB2 converts a very small portion of the energy generated by thepiezoelectric generator to operate the Safety Programmable Feature andcharges the capacitor C2. The energy stored in the capacitor C2 ismeasured by the resistor R2 and discharge resistor R16. The voltage atC2 (VC2) is compared with (VT1) at the midpoint of R4 and R5. When VC2is higher than VT1, the output of IC1 become transitions to a high stateand sets flip-flop IC3 and the flip-flop output Q transitions to a highstate which causes switching transistor T1 to open and not allow powerfrom reaching the initiator.

The initiator trigger mode operates in a similar fashion except that thetime constant of R3 and C3 and bleed resistor R15 is significantlygreater than the time constant of the Safety Programmable Feature.Similar to the operation of IC1, IC2 verifies that the voltage at C3(VC3) is greater than the voltage VT2. When this occurs the output ofIC2 transitions to a high state and causes switching transistor T2 toconduct and power the initiator. Note that this could only happen if thetransistor T1 is enabled to conduct (IC1 output, Q, is low).

The logic circuits IC3 and IC4 operate to ensure that the initiatorcannot be activated when accidental energy is generated by thepiezoelectric element, such as during an accidental drop, transportationvibration or other handling situations. The sequence of operation is asfollows: when the power first turns on, IC3 is reset by the OR circuit,this ensures that IC3 is now ready to detect accidental energy. Notethat this enables T1 to provide power to T2. However, switchingtransistor T2 is open which prevents T2 from powering the initiator ofthe battery. The function of the OR circuit is to initialize IC3 whenthe power first turns on and also to initialize IC3 when an all-firesignal occurs. Initializing IC3 will allow the firing circuit comprisedof switching transistor T1 and T2 to be able to power the initiator.

The overall functionality of the electrically initiated inertial ignitercircuitry is controlled by the Safety Programmable Feature (SPF) timeconstant and by the Initiation Trigger Mode (ITM) time function. Forexample, for the aforementioned no-fire and all-fire requirements, theSPF time constant is 0.5 msec and the ITM time constant is 15 msec. Thusthe safety feature will always occur first as shown in FIG. 3. Insituations such as transportation of the device in which the thermalbattery or the like is mounted, the device will be subjected tocontinuing vibration or vibration like oscillatory loading. In suchsituations, when the vibration continues, the present device would stillprovide for safety and prevents the initiator from being powered. Thesafety cushion is governed by a time constant of 14.5 msec, which iscontrolled by both R2 and R3.

FIG. 4 shows the diagram of another possible design of the piezoelectricelement powered electronics circuitry with programmable initiation timedelay feature for use in the disclosed electrically initiated inertialigniters. This design includes an integrated capability to delay theinitiation signal by a selected (programmed) amount of time, which couldbe in seconds and even minutes or more.

In the design shown in FIG. 4, power stored in power supply capacitor C1is harvested similarly from the at least one piezoelectric element andrectified by the bridge rectifier B1. The voltage at C1 rises to theoperational value and it is now ready to start powering the electronics,however, during the transitional state it is very important that thecomparator IC1 and IC2, and the OR gate be reset to its desired outputvalue. Capacitors C6 and C7, stabilize and reset IC1 and IC2,respectively, and capacitor C4 resets the IC3, which ensures thatswitching transistor T1 is ready for operation. A second enhancement ofthe design shown in FIG. 4 compared to that of the design shown in FIG.2 is related to the safe operation of the rectified output of the atleast one piezoelectric element at the bridge rectifiers output. DiodesD1, D3 and D4 are clamping and transient suppression diodes. Thesedevices ensure that high transient values of voltages produced by thepiezoelectric elements do not reach the electronic circuits.

In the event detection and logic circuitry of FIG. 4, a programmabletime delay capability to delay the signal to initiate the igniter isalso incorporated. In this circuitry design, IC4, the resistor R17 andthe capacitor C9 provide the time constant for the output of IC4 at R18to provide a delayed output to the igniter initiator circuit. Thedelayed output is determined by the values of R17 and C9. This circuitryobviously offers for both non-delayed as well as delayed outputdepending on the application. Obviously any other programmable timingdevice may be used instead.

In certain applications such as medium caliber projectiles, the firingacceleration is very high, for example up to 55,000 Gs and even higher,therefore significantly higher than any accidental accelerations thatmay be experienced due to dropping. In addition, the volume availablefor the thermal battery and its igniter is very small.

For such applications, it is preferable that the battery be kept in itsinactive state throughout the gun launch and until the accelerationforces resulting from setback and set forward have been significantlyabated. For this reason, it is advantageous that initiation of thethermal battery be delayed after launch until the projectile has exitedthe gun barrel. For such applications, the event detection, safety andignition electronics and logic and initiation time delay circuitry canbe significantly simplified.

FIG. 5 shows a design of a circuit that will measure the setbackacceleration by means of the at least one piezoelectric element. Thesignal produced by the piezoelectric element due to the setbackacceleration is rectified and monitored by IC1 for peak amplitude andduration. These two parameters create a voltage (VC2) which will becompared by IC1. When voltage VC2 becomes higher than voltage VT1, IC1will output a voltage which will reset IC2. At reset, IC2 will initiatea count of time which will be governed by the value of resistor R6 andcapacitor C3. The output of IC2 will be buffered by switching transistorT1 which powers the initiator.

There are also military and civilian applications that require certainsensors be deployed and remain waiting for certain events for relativelylong periods of time, ranging from minutes to hours or even days. Toaccomplish this purpose, a new type of timer will be employed to providesuch a dynamic range (minutes to days) as shown in FIG. 6. IC2 can beprogrammed to deliver delay times from minutes to days by the use of abinary type counter which uses the clock generated by the parallelcombination of R6 and C3 and multiplying it by a binary count dependingon which output 2^(n) is used.

In the circuitry shown in FIG. 6, the piezoelectric element will detecta launch or impact induced acceleration and/or deceleration, and thesignal produced by the launch and/or impact forces will be rectified anddetected by R1 and C2. The time constant provided by R1 and C2 will testthe signal from the piezoelectric element for duration, and thecomparison of the threshold voltage VC2 compared with VT1 will test thesignal for amplitude threshold. When the threshold has been detected,IC1 will reset the binary counter IC2 which will start counting time.When the selected time delay has been reached, the output of counterwill switch T1, upon which the initiator is powered.

The block diagram of FIG. 7 shows the general schematics of anotherembodiment of electrically initiated inertial igniters. In this class ofigniters, at least one piezoelectric element is used to generate acharge (electrical energy) in response to the acceleration and/ordeceleration profile that it experiences due to all no-fire and all-fireevents. The charge generated by the piezoelectric element is then usedto power the detection and safety electronics and logic circuitry andpossibly partially the detonation capacitor and its activationcircuitry, as described later in this disclosure. This class of conceptsare similar to the previous class of electrically initiated inertialigniter embodiments shown in FIG. 1, with the main difference being thatthe electrical energy required to heat the wire electrode probe toinitiate ignition of the pyrotechnic paper is provided mainly by areserve micro-power battery, preferably fabricated on the aforementionedlogic-based detection and switching circuitry chip, therebysignificantly reducing the amount of power that the at least onepiezoelectric element has to produce. In addition, since the energydensity of the reserve battery is generally significantly higher thanthat of the piezoelectric elements, the resulting electrically initiatedinertial battery is also expected to be smaller.

In this class of electrically initiated inertial igniter embodiments,essentially the same event detection, safety and ignition initiationelectronics and logic circuitry described for the aforementioned firstclass of electrically initiated inertial igniters shown in FIG. 1 isemployed with the exception that the power to initiate the ignition ofthe pyrotechnics comes mostly from the micro-power battery rather thanthe piezoelectric generator. As a result, more piezoelectric generatedpower is available to power the electronics and logic circuitry; therebyit is possible to add more safety features and even active elements tothe circuitry. More sophisticated detection schemes and more layers ofsafety may also become possible to add to the igniter electronics.

One type of reserve micro-power battery that is suitable for the presentapplication is micro-batteries in which the electrode assembly is keptdry and away from the active liquid electrolyte by means of anano-structured and super-hydrophobic membrane from mPhase Technologies,Inc., 150 Clove Road 11th Floor, Little Falls, N.J. 07424. Then using aphenomenon called electro-wetting the electrolyte can be triggered by avoltage pulse to flow through the membrane and initiate theelectrochemical energy generation. Such batteries have been fabricatedwith different chemistries.

In this class of electrically initiated inertial igniter embodiments,when the aforementioned event detection electronics circuitry and logic(such as those shown in FIGS. 2 and 4-6) detects the all-fire event, thecircuit would then switch the required voltage to trigger and activatethe reserve micro-power cell. In this concept, the piezoelectric elementmust only provide enough energy to the capacitor so that the requiredvoltage is generated in the capacitor for activation of the reservebattery. For this purpose and for the aforementioned reserve micro-powercell, the capacitor may have to provide a brief voltage pulse ofapproximately 50 milliseconds duration of between 30-70 volts. It isimportant to note that the triggering activation voltages required forelectrowetting technique to activate the reserve power cell requiresnegligible current from the storage capacitor.

The expected size and volume of the class of electrically initiatedinertial igniter embodiments shown in the block diagram of FIG. 7 isexpected to be less than those for the embodiments constructed based onthe block diagram of FIG. 1. This is expected to be the case since asignificantly smaller piezoelectric element will be needed for theactivation of the aforementioned reserve micro-power battery, whichcould be of the order of 1 mm² surface area and integrated onto thelogic and switching circuitry. In addition, the capacitor used fortriggering the reserve micro-power battery is expected to besignificantly smaller than that of the class of igniters shown in theblock diagram of FIG. 1. In addition, the power required to activate thereserve micro-power battery is minimal.

In an alternative embodiment shown in the block diagram of FIG. 7, anelectrically initiated thermal reserve micro-battery is used instead ofthe aforementioned micro-batteries in which the electrode assembly iskept dry and away from the active liquid electrolyte by means of anano-structured and super-hydrophobic membrane. The thermalmicro-battery can be very small since it has to provide a very smallamount of electrical energy which is quickly stored in the device powercapacitor (e.g., the capacitor C1 in FIGS. 2, 4-6). In fact, since ingeneral the thermal micro-battery is required to provide a very smallamount of electrical energy (usually 5-10 mJ to a maximum of 100-200 mJof electrical energy), the battery may be constructed with minimal oreven no insulation, thereby allowing it to be constructed in evensmaller packages.

The use of piezoelectric elements (preferably in stacked configuration)for energy harvesting in gun-fired munitions, mortars and the like iswell known in the art, such as at Rastegar, J., Murray, R., Pereira, C.,and Nguyen, H-L., “Novel Piezoelectric-Based Energy-Harvesting PowerSources for Gun-Fired Munitions,” SPIE 14th Annual InternationalSymposium on Smart Structures and Materials 6527-32 (2007); Rastegar,J., Murray, R., Pereira, C., and Nguyen, H-L., “Novel Impact-BasedPeak-Energy Locking Piezoelectric Generators for Munitions,” SPIE 14thAnnual International Symposium on Smart Structures and Materials 6527-31(2007); Rastegar, J., and Murray, R., “Novel Vibration-Based ElectricalEnergy Generators for Low and Variable Speed Turbo-Machinery,” SPIE 14thAnnual International Symposium on Smart Structures and Materials 6527-33(2007). Rastegar, J., Pereira, C., and H-L.; Nguyen,“Piezoelectric-Based Power Sources for Harvesting Energy from Platformswith Low Frequency Vibration,” SPIE 13th Annual International Symposiumon Smart Structures and Materials 6171-1 (2006) and U.S. PatentApplication Publication No. 2008/0129151 filed on Dec. 3, 2007. In suchenergy harvesting power sources that use piezoelectric elements, theprotection of the piezoelectric element from the harsh firingenvironment is essential and such methods are fully described in theabove provided references.

Another alternative embodiment is shown in the diagram of FIG. 8. Inthis programmable inertial ignition device embodiment diagram, thecircuitry design is divided into functional sections which wheninterconnected provide reliable methods to prevent unintentional andaccidental initiation to achieve the prescribed no-fire and all-firecondition. In the diagram of FIG. 8, each of the aforementionedfunctional sections (shown in FIG. 8 with dashed rectangles andindicated by capital letters A-G) are described separately as well ashow they are interconnected and function as a programmable inertialignition device. In this embodiment of the programmable inertialignition device, piezoelectric generators are also used to harvestenergy to power the device electronics and logics circuitry as well aspower the electrical initiator of the device.

Similar to the embodiments of FIGS. 2 and 4-6, at least onepiezoelectric-based generator (indicated as piezo in the diagrams ofFIGS. 2, 4-6 as well as 8) is provided. The generated electrical chargescan be rectified by the diodes bridges B1 and B2 (only one diode bridgecan be used and are shown in the above diagrams for ease of illustrationonly).

Section A:

When the piezoelectric generator is subjected to shock loading such asexperienced by setback and/or acceleration and/or is subjected tomechanical vibration, its output is rectified by the diode bridge B1 anda small amount of the generated electrical energy is used to begin tocharge a small capacitor [C2]. The voltage across C2 is regulated to afixed reference voltage [Vref.1]. The regulated voltage [Vref.1]provides power to logic circuits [IC1, IC2, IC3].

Sections B, C, F:

The electrical output of the piezoelectric generator also feeds thepower supply capacitor C1 (Section B) from diode bridge B2, which willcharge much slower than capacitor C2 due to its significantly largersize. The voltage across C1 will not power the initiator until itreaches a controlled value, as follows: IC3 monitors the voltage acrossC1 by means of resistors R6 and R7 (part of Section C). When the voltageat the (S) input of IC3 reaches approximately 0.7 Vref.1, latch deviceIC3 output will switch to logic 1. The output of IC3 will provide alogic 1 condition at input 2 of IC2 (Section F). IC3 will always beinitialized to a logic zero output when Vref.1 first comes on. Theinitialization is achieved by a very small burst of electrical energyfrom Vref.1 being fed to the reset (R) input of IC3 through capacitor C4and resistor R8. Capacitor C4 charges very quickly and its impedancebecomes infinite at full charge, therefore the voltage at the reset (R)pin of IC3 becomes zero in a few micro-seconds. The duration of thereset (R) pulse is directly controlled by C4*R8 (part of Section C).

Sections D, E, F:

The safety programmable feature (Section D) functions as previouslydescribed for the embodiments of FIGS. 2 and 4-6. In short, it uses theelectrical energy generated by the piezoelectric generator to charge thecapacitor C3. The capacitor C3 charges at a rate that is controlled byR1*C3. Resistor R2 leaks some of the charge built across C3, so that thevoltage across C3 does not build up unless a sustained and high amountof electrical energy is generated by the piezoelectric generator, i.e.,a large enough force is applied to the piezoelectric element longenough, as would be the case during the launch acceleration of munitions(corresponding to the all-fire condition). If the voltage across C3(Vc3) reaches the same value or higher value than the voltage across R5and D5 (Vref.2), then op-amp IC1 output will reach a logic 1. The diodeD5 is a clamping and transient suppression diode. The output of IC1 isdirectly connected to the input 1 of IC2.

Sections F, G:

When both input 1 and input 2 conditions are met (Section F), the outputof logic circuit IC2 will provide electrical energy to drive transistorT1 into saturation and therefore transistor T1 will operate as a switchthereby connecting the supply voltage across C1 (V supply) to theinitiation device (indicated as resistor R6). Note that switch T1 willnot connect “V supply” until it reaches a value of approximately0.7Vref.1.

In the embodiments, the initiator (e.g., indicated as resistor R6 in theembodiment of FIG. 8) was shown to be used. It is noted that during theinitiation process, the resistor R6 is heated up to initiate thepyrotechnic material that surrounds it. During this process, theresistor R6 filament or the like is burned, and thereby very lowresistance (usually in the order of a few Ohms) measured of the resistorR6 is significantly increased (usually by orders of magnitude) dependingon the pyrotechnic material used in the initiator. This change in theresistance of the initiator filament is readily detectable and can beused to determine if the initiator has been activated. For the exampleof the embodiment of FIG. 8, the resistance of the resistor R6 isreadily measured between the terminals 10 and 11 as shown in theschematic of Section G of the FIG. 8 circuitry that is redrawn in FIG.9.

It will be appreciated by those skilled in the art that in certainsituations, for example following certain accidents such as dropping ofmunitions or when subjected to electrostatic discharge or the like orfor health monitoring purposes, it is highly desirable for the user tobe able to determine if the thermal battery has been activated or notwithout the need to disassemble the munitions and perform testing suchas using x-rays to determine the activation state of the thermalbattery. The above embodiment allows the user to interrogate theactivation state of the thermal battery to determine if it has beenalready activated by measuring the resistance level of the initiator. Itis noted that even if the thermal battery has been accidentallyinitiated by means other than the activation of the initiator (resistorR6 in FIGS. 8 and 9), upon activation of the thermal battery pyrotechnicmaterials, the initiator resistor would still be burned and the state ofthe thermal battery activation can still be determined by the measuredchanges in the initiator electrical resistance.

It is a common practice in thermal batteries to use a single initiatorfor thermal battery activation, as was also described in theaforementioned embodiments. However, in certain applications when veryhigh initiation reliability is desired, two or more initiators (e.g.,similar to the initiator R6 in FIGS. 8 and 9) may be employed. Forexample, at least one additional initiator R6 a may be provided inparallel with the initiator R6 as shown in the modified schematic ofSection G of the circuitry of FIG. 8 as illustrated in the schematic ofFIG. 10. With the addition of the least one additional initiator R6 a,FIG. 10, by measuring the electrical resistance between the terminals 10and 11, it is readily determined if at least one of the initiatorresistors R6 or R6 a has burned, i.e., its electrical resistance hasbeen significantly increased, which indicates if the thermal battery hasbeen activated.

When more than one initiator is being used to increase thermal batteryactivation reliability, it is highly desirable to provide the additionalinitiators with independent circuitry, and when possible, independentsources of power and safety and logics circuitry as described for theembodiments of FIGS. 2, 4-6 and 8. When it is not possible to providesuch totally independent power source and circuitry, the at least oneadditional independent initiator circuitry needs to be powered by thesame device power supply capacitor (e.g., the power supply cap C1 ofSection B in FIG. 8). For the embodiment of FIG. 8 and with oneadditional independent initiator circuitry, the resulting Section Gcircuitry can be modified to that of FIG. 11. In FIG. 11, theaforementioned one additional independent initiator circuitry isindicated as Section Ga, and is shown to be constructed with identicalcomponents R3, T1 and initiator R6, but could obviously be constructedwith any other appropriate components and circuitry, and is connected tothe circuitry of the embodiment of FIG. 8 and its Section G as shown inFIG. 11.

It will be appreciated by those skilled in the art that for the latterembodiment shown in the schematic of FIG. 11, the more than one parallelinitiator R6 (in the Section G) and Rha (in the at least one Section Ga)may be employed, such as the one shown in FIG. 10.

It is also appreciated by those skilled in the art that the provision ofmore than one initiator in a thermal battery has many advantages,including the following:

-   -   1. By providing more than one initiator, particularly if it has        independent circuitry and when possible a totally independent        initiation unit with its own power source and safety and        initiation circuitry, the thermal batter activation reliability        is significantly increased.    -   2. With more than one initiator, the initiators can be        distributed in the thermal battery to ignite the thermal battery        pyrotechnic materials at more than one location. This capability        provides the means of achieving several objectives. Firstly,        since the thermal battery rise time (the time that it takes for        the battery to become functional following initial initiator        activation) is dependent on the time that it takes for the        thermal battery pyrotechnic (heat generating components) to burn        and melt the solid electrolyte, by igniting the thermal battery        pyrotechnic materials at more than one location, the total time        that it takes for the pyrotechnic material to be burned is        significantly reduced. As a result, the thermal battery becomes        fully functional faster, i.e., the thermal battery rise time is        significantly reduced. Fast rise time is a highly desirable        characteristic in certain munitions, e.g., when the thermal        battery power is required a very short time following firing.        Secondly, by distributing multiple initiators in the thermal        battery, a more uniform pattern of pyrotechnic material burn is        achieved in the thermal battery and, thereby avoiding        non-uniform heating and later cooling of the solid electrolyte,        thereby achieving a better thermal battery performance.

In the aforementioned embodiments, active material based elements suchas piezoelectric elements (FIGS. 1-2 and 4-8) can be used to generateelectrical energy by harvesting electrical energy from the firingacceleration. It is, however, appreciated by those skilled in the artthat other types of electrical generators such as coil and permanentmagnet type generators may also be used for this purpose. Such coil andpermanent magnet type electrical generators may be constructed toundergo linear or rotary or a combined linear and rotary motion,including a vibratory type of linear and rotary motions. In either case,the linear or rotary motion, including of vibratory type, are caused orinitiated by the firing event of the munitions in which the thermalbattery or the like equipped with such devices are mounted. As anexample, coil and permanent magnet type generators that are designed tooccupy relatively small volumes and generate electrical energy as aresult of firing setback and/or set-forward accelerations and some evenas a result of flight vibration and oscillatory motions are providedbelow.

In one embodiment, a magnet and coil generator 20 that forms a vibratingmass-spring system shown in the schematic of FIG. 12 is used to generateelectrical energy as a result of firing acceleration in the direction ofthe arrow 21. The magnet and coil generator 20 is attached to thestructure 22 of the device (generally the structure of the initiator),and consists of a coil 23 and magnet 24 elements, with the magnet 24element (constructed with at least one permanent magnet) is preferablyused to function as a mass element that together with the spring element25 form a vibrating mass-spring unit, that is attached to the structure22 of the initiator device. Then as the munitions using any one of theinitiator embodiments shown in FIGS. 1-2 and 4-8 is fired, the firingsetback acceleration acts on the mass (magnet portion) 24 of thegenerator 20, causing the spring element 25 to be deflected a distanceindicated by 26, bringing the mass to the position 27, as indicated bydashed lines in FIG. 12. As the munition accelerates, such as after themunition exits the barrel, the mass-spring unit (elements 25 and 26,respectively) will begin to vibrate up and down in the direction shownby the arrows 28, and the generator will generate electrical energy asis well known in the art. It is noted that in general the firingset-forward acceleration and vibration of the munitions during theflight would also cause vibration of the generator mass-spring unit,thereby cause the generator 20 to generate more electrical energy. Thespring element 25 is preferably made with at least 3 helical strands tominimize the tendency of the mass-spring element to displace laterallyor bend to the side during longitudinal displacement and vibration inthe direction of the arrow 21.

It will be appreciated by those skilled in the art that since electricalenergy is generated in the coils 23, the vibrating component of suchmagnet and coil generators can be the permanent magnet(s) 24 of themagnet and coil generator 20. As a result, the generator output wiresare fixed to the structure 22 of the device and the chances of thembreaking is minimized.

In another embodiment, the spring element 25 is preloaded and thepermanent magnet(s) 24 (mass element) of the mass-spring unit of themagnet and coil generator 20 is locked in its displaced position 27shown by dashed lines in FIG. 12 by at least one locking element that isprovided to lock the spring 25 in its compressed (preloaded)configuration. Then during firing of the projectile, the munitionsstructure to which the present device magnet and coil generator 20 isrigidly attached is accelerated in the direction of the arrow 21,causing the aforementioned at least one locking element to releasepermanent magnet(s) 24 (mass element) of the mass-spring unit of themagnet and coil generator 20. Once the permanent magnet(s) 24 (masselement) of the mass-spring unit of the magnet and coil generator 20 isreleased, the mechanical potential energy stored in the spring 25, i.e.,the mechanical potential energy stored in the “mechanical reserve powersources” 20, is released. The released mechanical potential energy willthen cause the mass-spring unit) to vibrate, thereby causing the magnetand coil generator 20 to generate electrical energy. Such lockingelements for locking preloaded mass-spring units (here, for thepermanent magnet(s) 24, i.e., the mass element, of the mass-spring unitof the magnet and coil generator 20) that lock preloaded linearly orrotationally or flexural vibrating units and that are released due toaxial acceleration (setback or set-forward acceleration in munitions),or rotational (spin) accelerations or spin rate (due to centrifugalforce) are fully described in the U.S. Pat. No. 8,183,746, the entirecontents of which is incorporated herein by reference.

In another alternative embodiment, the aforementioned safety andall-fire detection circuitry (such as the “safety programmable feature”of FIG. 8 and marked “D”) is provided with additional beneficialfeatures herein being described. In this embodiment, the generalcircuitry of the safety and all-fire detection is as shown in FIG. 13.The circuitry is considered to be passive since it does not require anyexternal source of power or batteries or other similar sources ofchemical or externally charged power sources for its operation. In amanner similar to those described for the previous safety and all-firedetection circuitry, the firing setback or other shock loading and/orvibrations of the device in which the present circuitry is used wouldinduce charges in the piezoelectric (preferably stack) element. Thepresent circuitry is designed to differentiate firing setback inducedshock (high-G accelerations with relatively long duration) from allother no-fire accelerations such as high-G but short duration pulse(s),relatively low peak G but long term vibration loading such asexperienced during transportation and the like.

In the safety and all-fire detection circuitry of FIG. 13, electricalenergy (charge) is provided by at least one piezoelectric (preferablystack) element. All-fire setback condition is detected by the voltagelevel of the capacitor C1 while the circuitry prevents the charging ofthe capacitor C1 to the prescribed voltage level if the generatedpiezoelectric charges are due to the aforementioned no-fire conditionsas described below.

In the safety and all-fire detection circuitry embodiment of FIG. 13,the diode D1 (preferably a Schottky or a similar diode with a lowforward voltage drop and a very fast switching action is used as arectifier. The indicated feature of the diode D1 reduces energy loss inthe circuitry. The indicated diode D1 also has a high backward leakage,which is used as a safety feature in the present embodiment fordischarging collected charges in the capacitor C1 when the voltage ofthe piezoelectric element drops below the prescribed all-fire voltagelevel.

After rectified, the current due to the charges generated by thepiezoelectric element passes through diode Z1 (preferably a Zener or asimilar diode) and resistor R1 to charge the capacitor C1 and also passthrough resistors R2 and R3 to the ground. During this time, the diodeD2 is under reverse bias, thereby passing a very small amount ofcurrent. The voltage on the capacitor C1 indicates the amount of energygenerated by the piezoelectric element due to its (shock or vibration)loading, less the amount of energy drainage through the resistors R2 andR3 and the losses in the diode Z1 and smaller amounts in the remainingcircuit elements. The resistors R2 and R3 also act as a programmabledivider that can be used to adjust the output voltage levelcorresponding to the all-fire condition as demanded by thedevice/circuitry at the circuitry output shown in FIG. 13. It is alsonoted that the output and ground can also be used as a differentialoutput.

When a device using the circuitry shown in FIG. 13 is subjected to arelatively short duration shock loading such as due to accidentaldropping, the piezoelectric element would generate relatively highvoltage pulses with very short duration. The generated voltages may evenbe higher than the voltage level that are generated as the device issubjected to the prescribed all-fire setback acceleration, but theduration of such pulses is significantly shorter than those of theall-fire setback acceleration pulse. For example, an all-fireacceleration may be around 900 G with 10 msec of duration while anaccidental drop may cause a shock loading of up to 2,000 G but for avery short duration of less than 0.5 msec. In the present circuitryembodiment, the capacitor C1 and the resistor R1 are sized such that theresulting charging time constant (R1C1) for the capacitor C1 issignificantly longer than such “high voltage and short duration” pulses,thereby ensuring that the capacitor C1 is not charged to theaforementioned “all-fire voltage level” due to any no-fire shock loadingevent. In addition, to ensure that the charges due to several such “highvoltage and short duration” pulses do not accumulate in the capacitor C1and provide a false “all-fire voltage level” indication, the diode D2 isprovided to discharge all accumulated charges in the capacitor C1 oncethe piezoelectric voltage drops below the voltage level on C1.

In certain application, however, when the piezoelectric voltage drops,the amount of discharge through the diode D2 is desired to be limited toa drop of the capacitor C1 voltage to certain threshold. The voltagethreshold may be desired, for example, for allowing the voltage at thecircuitry OUTPUT not to drop below certain limit. As an example andwithout intending to indicate any limitation on the use of othercomponents and circuitry to perform the same functionality, such a goalcan be readily achieved by the addition of a Zener diode Z2 between thediodes D1 and D2 as shown in the alternative “safety and all-firedetection circuitry” embodiment of FIG. 19. As a result, piezoelectricvoltage drops, the charges accumulated in the capacitor C1 is dischargedthrough the diode D2, but only to the breakdown voltage level of theZener diode Z2 instead of dropping to essentially the voltage level ofthe piezoelectric element.

In addition, in both the circuits of FIGS. 13 and 19, when the diode D2is under reverse bias, it passes a very small amount of current. If incertain applications the amount of this current is needed to be reduced,this can be readily accomplished by the addition of the serial resistorR6 as shown in the schematic of FIG. 19A. Then in the resulting circuit,when the diode D2 is under forward bias, the resistor R6 would controlthe time that it would take for the charges collected on the capacitorC1 to be discharged back to the piezoelectric element.

It is noted that leaking through resistors R2 and R3 is also used tolengthen the amount of time that is needed for the piezoelectric elementto charge the capacitor C1. This capability provides a simple tool toreadily adjust (“program”) the device to the desired “all-fire”condition. The leakage through resistors R2 and R3 would also provideadditional means of ensuring that the aforementioned high voltage andshort duration pulses do not accumulate charge in the capacitor C1 totrigger a false all-fire detection signal.

It is also noted that vibration loading (usually with peak G loadingsthat are usually significantly lower than those of accidental drops orthe like) for long periods of time such as those experienced duringtransportation or other similar conditions, even if they are accompaniedwith aforementioned higher G but short duration shock loading pulses aresimilarly rejected by the Zener diode Z1 and the leaking resistors R2and R3. The breakdown voltage of the Zener diode Z1 is generallyselected depending on the selected all-fire indicating voltage of thecapacitor C1.

The piezoelectric element powered safety and all-fire detectioncircuitry shown in FIGS. 13, 19 and 19A provide a voltage at theindicated output that can be monitored by the user device/circuitry todetect no-fire condition based on the prescribed (“programmed”) all-firesetback acceleration condition. In the following, the method of usingthe safety and all-fire detection circuitry embodiment of FIG. 13 orFIG. 19 or 19A to design passive initiators for igniting pyrotechnicmaterial or the like is described. Examples of other applications formunitions all-fire condition detection and other commercial andindustrial applications in which a prescribed shock or vibration loadingis to be safely detected are described later in this disclosure.

A method of using the safety and all-fire detection circuitry embodimentof FIG. 13 (or similarly the safety and all-fire detection circuitryembodiment of FIG. 19 or 19A) to design passive initiators forpyrotechnic material or the like is herein described and examples of itsimplementation are provided. The safety and all-fire detection circuitryof the embodiment of FIG. 13 is redrawn in FIG. 14. In the presentmethod, the circuit output is connected to the indicated “output voltagethreshold detection and switching element”, which is designed to detectwhen the output voltage threshold corresponding to the prescribedall-fire condition has been reached. When the all-fire voltage thresholdis detected, the “output voltage threshold detection and switchingelement” would then close the indicated circuit and allow direct flow ofcurrent from the piezoelectric element through the indicated “initiatorbridge wire” to the ground. The initiator bridge wires currently usedare very low resistance (commonly around 1-3 Ohm) bridge wires that areheated by the passing current, which would then usually ignite certain(usually primary) pyrotechnic material. Initiator bridge wires ofdifferent types such as those made out of ultra-thin wires or wiresprinted/deposited/etched on certain substrate or semi-conductor typesuch as those fabricated using semi-conductor manufacturing processesare commonly used in electrical initiators and could be used in thepresent embodiment.

The “output voltage threshold detection and switching element” may bedesigned in a number of ways and with and without external power. In themunitions applications, however, one of the main objectives is safety,i.e., total or nearly total elimination of the chances that initiationcould occur in the absence of all-fire detection. The other objectivesin munitions application include passive circuitry, i.e., the initiatorcircuitry not requiring external power; and miniaturization, whichrequires very low power circuitry that can be powered with very smallpiezoelectric elements. The following embodiments are examples ofpassive electrical initiators for pyrotechnic material or the likeconstructed with the safety and all-fire detection circuitry embodimentof FIG. 13.

The method of using the safety and all-fire detection circuitryembodiment of FIG. 13 to design passive initiators for pyrotechnicmaterial or the like is herein described and examples of itsimplementation are provided. The safety and all-fire detection circuitryof the embodiment of FIG. 13 is redrawn in FIG. 14. In the presentmethod, the circuit output is connected to the indicated “output voltagethreshold detection and switching element”, which is designed to detectwhen the output voltage threshold corresponding to the prescribedall-fire condition has been reached. When the all-fire voltage thresholdis detected, the “output voltage threshold detection and switchingelement” would then close the indicated circuit and allow direct flow ofcurrent from the piezoelectric element through the indicated “initiatorbridge wire” to the ground. The initiator bridge wires currently usedare very low resistance (commonly around 1-3 Ohm) bridge wires that areheated by the passing current, which would then usually ignite certain(usually primary) pyrotechnic material. Initiator bridge wires ofdifferent types such as those made out of ultra-thin wires or wiresprinted/deposited/etched on certain substrate or semi-conductor typethose fabricated using semi-conductor manufacturing processes arecommonly used in electrical initiators and could be used in the presentembodiment.

As was previously indicated, for most munitions and other similarapplications, the “output voltage threshold detection and switchingelement” of the embodiment of FIG. 14 is to be designed with a very highlevel of safety, i.e., for total or nearly total elimination of thechances that initiation occurs in the absence of all-fire condition.Other important objectives in munitions and other similar applicationsinclude passive circuitry, i.e., the initiator circuitry not requiringexternal power; and miniaturization capability, which requires very lowpower circuitry that can be powered with very small piezoelectricelements. The following two basic embodiments are examples of theimplementation of the embodiment of FIG. 14 for such passive electricalinitiators for pyrotechnic material or the like that are constructedwith the safety and all-fire detection circuitry embodiment of FIG. 13.

The first embodiment of the passive initiators for pyrotechnic materialor the like with the above safety and low power characteristics whichmakes it particularly suitable for munitions and other similar initiatorapplications is shown in FIG. 15. In this embodiment, the safety andall-fire detection circuitry embodiment of FIG. 13 is provided with the“output voltage threshold detection and switching element” described forthe embodiment of FIG. 14 designed with the circuitry shown inside thebox with dashed lines. As can be seen in the “output voltage thresholddetection and switching element” shown in FIG. 15, by appropriatelyselecting the component parameters of the circuitry, when the voltage atthe OUTPUT of the safety and all-fire detection circuitry (FIGS. 13 and15) reaches the prescribed all-fire threshold, the N-MOS (indicated asQ1 in FIG. 15) is switched on. During this switching-on process, thevoltage on the resistor R4 increases and produces a current IBE on NPNtransistor (indicated as Q3 in FIG. 15), in the direction of the arrowat B). The NPN transistor Q3 amplifies the current and introducescurrent IBE on PNP transistor Q2, while the PNP transistor Q2 amplifiesthe current and sends it back to the NPN transistor Q3. This positivefeedback configuration of the two transistors Q2 and Q3 at certainsaturates the two transistors, making them act as a “switch” that hasbeen closed between the points 30 and 31 in the circuit of FIG. 15,thereby allowing the charges generated by the piezoelectric element tobe discharged through the indicated “bridge wire” to the ground (GND).The very low resistance initiator bridge wire is then heated by thepassing current, which would then ignite the provided (usually primary)pyrotechnic material.

It will be appreciated by those skilled in the art that when thetransistors Q2 and Q3 saturate, the closed circuit between the points 30and 31 stay closed since the positive feedback between the transistorsQ2 and Q3 maintains the discharging current loop from the piezoelectricelement through the bridge wire to the ground. This is an importantfeature of the current embodiment since the safety and the “safety andall-fire detection circuitry” portion (embodiment of FIG. 13) of thepassive initiators embodiment of FIG. 15 is also powered by the devicepiezoelectric element, which means the detected all-fire signal voltage(at the indicated OUTPUT) will drop instantly as the transistors Q2 andQ3 saturate and the circuit (“switch”) between the points 30 and 31 isclosed and the piezoelectric element charges begin to discharge throughthe “bridge wire” to the ground. It will be appreciated by those skilledin the art that if the current to be passed through the “bridge wire”would have been routed through the indicated OUTPUT of the “safety andall-fire detection circuitry” portion of the device, the drop of thevoltage at the OUTPUT point below the all-fire threshold level wouldhave again suddenly blocked the current from reaching the “bridge wire”by reverting the “safety and all-fire detection circuitry” portion backto its no-fire state.

It will be appreciated by those skilled in the art that in the circuitryof FIG. 15, the resistance of the resistor R4 determines the inputimpedance of the bridge wire initiator circuitry. The resistor R4resistance level is very important for reducing the sensitivity of thepositive feedback against noise such as electromagenetic interference(EMI) and electromagnetic pulse (EMP) and the like. In a slightlymodified circuitry, RC filters may be added between Q2 and Q3 to controlthe gain of positive feedback.

In a second embodiment of the passive initiators for pyrotechnicmaterial or the like with the above safety and low powercharacteristics, when the noise due to sources such as electromageneticinterference (EMI) and electromagnetic pulse (EMP) and other internaland external sources is either very low or has been taken care of usingappropriate shielding and filtering, then a Silicon Controlled Rectifier(SCR) may be used in place of the two transistors Q2 and Q3 in theembodiment of FIG. 14 as shown in the circuitry of FIG. 16. The SCR is aswitch driven by gate current and would stay enabled while a current isbeing passed through it.

Then as was described for the embodiment of FIG. 15, by appropriatelyselecting the component parameters of the “output voltage thresholddetection and switching element” portion of the circuitry shown in FIG.16, when the voltage at the OUTPUT of the safety and all-fire detectioncircuitry (FIGS. 13 and 16) reaches the prescribed all-fire threshold,the N-MOS (indicated as Q1 in FIGS. 15 and 16) is switched on. When theN-MOS (Q1) is switched on, the SCR receives enough gate current IG andbecomes a path to release all the charges from the piezoelectric elementthrough the bridge wire to the ground (GND). The SCR will stay enableduntil essentially all charges from the piezoelectric element aredischarged and the aforementioned current IG is diminished. As a result,the flow of charges from the piezoelectric element through the bridgewire cannot be interrupted. The very low resistance initiator bridgewire is then heated by the passing current, which would then ignite theprovided (usually primary) pyrotechnic material.

As was previously indicated, the piezoelectric element powered safetyand all-fire detection circuitry shown in FIG. 13 provides a voltage atthe indicated output that can be monitored by the user device/circuitryto detect no-fire condition based on the prescribed (“programmed”)all-fire setback acceleration condition. The method of using theall-fire detection circuitry embodiment of FIG. 13 to design passiveinitiators for igniting pyrotechnic material or the like and a number ofits practical implementation embodiments that are particularly suitablefor munitions applications were disclosed above. In the following, themethod of using the safety and all-fire detection circuitry embodimentof FIG. 13 to design “passive all-fire detection sensors” that wouldoutput a signal indicating that a prescribed all-fire condition or othersimilar events such as lower level impact or shock or sudden jerk oroutset of vibration or the like has been detected is described. Aspreviously indicated, these devices differentiate no-fire conditionssuch as accidental drops which can induce high G levels with shortdurations and transportation related shock and vibration loadings. Theoutput signal could be of many different types, a few of which aredescribed below, but other types appropriate for matching a user need,for example a flag, a switch and hold or the like, can generally beaccommodated. The present devices are considered to be passive sincethey do not require external power sources for their operation. In thepresent devices, the sensory information as well as electrical energy topower the electronic circuitry is provided by an appropriately sizedpiezoelectric element(s).

The safety and all-fire detection circuitry shown in FIG. 13 may be useddirectly to provide a voltage output that can be monitored by the userdevice/circuitry to detect all-fire condition based on the prescribedall-fire setback acceleration and the selected circuit elements. It isnoted that in general, the circuit elements are selected to minimize thepower consumption and thereby minimize the size of the piezoelectricassembly. For the same reason, the voltage monitoring device is alsodesired to have very high impedance.

The safety and all-fire detection circuitry shown in FIG. 13 may also beused with other added logic circuitry and elements to provide thedesired sensory information or sensory based actions such as theinitiation described for the embodiments of FIGS. 14-16 and otherpurposes such as to provide a signal flag; provide multiple signal flagswhen different levels of firing setback accelerations are detected; oractivate a switching device; or initiate the process of storingelectrical energy in a storage device such as a capacitor; or numerousother applications.

The method of designing the aforementioned “passive all-fire detectionsensors” is shown in the schematic of FIG. 17. In FIG. 17, the “passiveall-fire detection circuitry” portion of the circuitry enclosed bydashed lines. In this method, safety and all-fire detection circuitryshown in FIG. 13 is used provide logic signal flags when one or morefiring setback acceleration (shock) levels are detected. In theschematic of FIG. 17, the circuitry provides logic signal flags for oneor multiple firing setback acceleration levels (in the schematic of FIG.17 for two firing setback or the like acceleration levels) that can bedirectly read by other devices through digital ports. In the circuitryof FIG. 17, this capability is provided by the addition of the indicatedlogic level comparators U1 and U2 to compare the outputs OUTPUT 1 andOUTPUT 2 of the safety and all-fire detection circuitry shown in FIG. 13(with the addition of the voltage divider resistor R4 for the indicationof the second prescribed firing setback or the like acceleration levelindicated by OUTPUT 2) with the output level from a reference voltagesupply (U3) and generate compatible logic level outputs (preferably alogic signal voltage level appropriate for the detecting deviceelectronics). It will be appreciated by those skilled in the art that byproviding appropriate additional resistors (in addition to the resistorR4), other voltage levels (i.e., other firing setback or the likeacceleration levels) may be similarly detected.

It will be appreciated by those skilled in the art that there are manymethods and means to implement the aforementioned logic level comparatorcomponents of the passive all-fire detection sensor circuitry of FIG. 17such as the use of an op-amp. However, in a preferred embodiment,Schmitt triggers are used since in these devices the threshold voltageto which the signal is compared depends on the state of output. Thisfeature is particularly advantageous when the signal rises (or falls)through the switching region in a “noisy” or fluctuating manner since aSchmitt trigger would provide only one switching output, unless thefluctuations are of amplitudes greater than its threshold range.

A typical preferred implementation of the passive all-fire detectionsensor circuitry of FIG. 17 with the aforementioned Schmitt triggers fordetection of two firing setback acceleration (shock) levels is shown inthe schematic of FIG. 18. This embodiment of the present “passiveall-fire detection sensors” is also designed to operate with very lowpower to make it possible to package the device in a very small volume.In this embodiment, the “passive all-fire detection circuitry” enclosedby dashed lines is designed to provide logic signal flag(s) for one ormultiple firing setback acceleration (shock) levels, in the particularcase of the embodiment of FIG. 18 for two firing setback acceleration(shock) levels, that can be directly read/detected by other devices,preferably through digital ports.

It will be appreciated by those skilled in the art that in the safetyand all-fire detection circuitry shown in FIG. 13, the proportion of theresistors R2 and R3 were indicated to be selected to provide the desiredvoltage level at the indicated OUTPUT when the voltage on the capacitorC1 reaches the level corresponding to the prescribed all-fire setbackacceleration (shock) level. The voltage at the circuit OUTPUT can thenbe designed to correspond to any desired voltage level for detection inthe case of the present embodiment or any other similar purposes. In asimilar manner, the proportions of the resistors R2, R3 and R4 areselected to provide the desired voltage level at the indicated OUTPUT1(FIGS. 17 and 18) when the voltage on the capacitor C1 reaches the levelcorresponding to the prescribed all-fire setback acceleration (shock)level. However, if the experienced all-fire setback acceleration (shock)level is higher than that indicated by the OUTPUT1, then when thevoltage at the capacitor C1 reached to a voltage corresponding to thehigher (second) voltage level corresponding to the higher (second)all-fire setback acceleration (shock) level, then the voltage at theindicated OUTPUT2 would increase and reach a higher (second) desiredvoltage level (FIGS. 17 and 18). The voltage level at the OUTPUT2 wouldthen provide the indication of the second (higher) all-fire setbackacceleration (shock) level having been reached. It will be appreciatedby those skilled in the art that more resistors may be similarly provide(in series with the resistors R2, R3 and R4) to divide the voltage atthe capacitor C1 to more different voltage levels, each corresponding toincreasing levels of all-fire setback acceleration (shock) levelsexperienced by the disclosed passive all-fire detection sensors of theembodiments of FIGS. 17 and 18.

It will be appreciated by those skilled in the art that typical currentlogic signal voltage levels are 3.3V and 5V CMOS level or +/−12V. Toprovide such compatible voltage levels at the OUTPUT1 and OUTPUT2 (andother output levels if present) in the embodiments of FIGS. 17 and 18 orthe like; a reference voltage supply is also required. Such a referencevoltage supply may be provided in a number of ways. In a preferredembodiment shown in the schematic of FIG. 18, the Zener diode Z2together with the current limiting resistor R5 and the capacitor C2provide a desired reference voltage level to the Schmitt triggers U1 andU2 from the rectified piezoelectric output. Here the low leakage Zenerdiode Z2 clips the reference voltage to its breakdown voltage to providea precise desired reference voltage level. The Schmitt triggers U1 andU2 also reduce noise impact on the high input impedance logic gates ofthe user provided circuitry.

The operation of the “safety and all-fire detection circuitry”embodiments of FIGS. 13, 19 and 19A were described for the detection ofprescribed all-fire conditions in terms of the munitions firing setbackacceleration level and its duration. All other no-fire conditions, suchas lower level shock loading and vibration due to transportation orshort duration shock loading due to accidental drops and other similarevents and high noise are differentiated from the prescribed all-firecondition. The operation of the “safety and all-fire detectioncircuitry” embodiments of FIGS. 13, 19 and 19A when used with an “outputvoltage threshold detection and switching element” to allow direct flowof current from the piezoelectric element through the indicated“initiator bridge wire” (or any other electrical or electronic or thelike elements) to the ground as previously described for the embodimentsof FIGS. 14-16 and the operation of the passive “passive all-firedetection sensor” embodiments of FIGS. 17 and 18 were also described forprescribed munitions all-fire setback accelerations level and duration(all-fire condition) detection and operation while rejecting allaforementioned “no-fire” conditions. It is, however, appreciated bythose skilled in the art that any one of the above embodiments may alsobe used to detect other shock or vibration or acoustic noise or othersimilar acceleration levels instead of the all-fire setback acceleration(shock) levels and similarly operate the circuitry of embodiments ofFIGS. 13-19 and 19A.

In certain munitions applications, instead of detecting firing setback(shock) loading, it is highly desirable to provide a sensor that candetect one or more impacts of the munitions with the target and theirtime history. The munitions may encounter more than one impact, forexample, by impacting more than one barrier such as a building wall orceiling or other multi-layer structures provided to protect the target.In such applications, particularly when multiple impacts areencountered, it is usually also desired to for the munitions electronicsand logics circuitry and/or processor(s) to also have an indication ofthe impact time, duration and level. In such applications, the munitionsis generally provided with the source of electrical energy such ascharged capacitors or super-capacitors and/or chemical batteries and/orelectrical energy generated by devices harvesting energy from theenvironment such as shock loading or vibration or vibratory motions orthe like to power its microprocessor(s), electronic and logics circuitryand other electrically powered devices.

In the following, the methods of employing the aforementioned “safetyand all-fire detection circuitry” of embodiments of FIG. 13 or 19 or 19Ato design sensors for detecting one or more target impact (shock)loading and preferably their impact levels as a function of time aredescribed and examples of their preferred implementation are provided.Hereinafter in the present disclosure such sensors are generallyreferred to as the “impact detection and time history sensors”. It willbe appreciated by those skilled in the art that such a sensor which isdesigned to detect (usually significant) barriers, are in fact alsodetecting (relatively) free space (or void) between such barriers, andare therefore hereinafter may also be referred to as “void detectors” or“void counter”.

The method of designing the aforementioned “impact detection and timehistory sensors” (or alternatively indicated as “void detector” or “voidcounter”) is described with the schematic shown in FIG. 20. As can beobserved, the sensor employs the previously described “safety andall-fire detection circuitry” of the embodiment of FIG. 13 (or itsalternative embodiments of FIGS. 19 and 19A). In the schematic of FIG.20, the “impact detection and time history sensor” circuitry portion ofthe sensor embodiment is shown enclosed by dashed lines. In this method,the “safety and all-fire detection circuitry” of the embodiment of FIG.13 (or its alternative embodiments of 19 and 19A) is to detect targetimpact by the munitions in which the sensor is mounted and “record” thetime history of the detected impacts. The process of detecting impact isidentical to those described for the embodiments of FIGS. 13, 19 and 19Afor the detection of all-fire setback (shock) acceleration except thatall-fire setback acceleration is applied to munitions in the directionof their travel for them to gain velocity while the target impact-baseddeceleration (hereinafter, acceleration and deceleration may be usedinterchangeably—i.e., without regard to the sign of the rate of changeof the sensor velocity) is essentially in the opposite direction andacts to decelerate the munitions along its path of travel (neglectingany generally present sideway acceleration due to an angled targetimpact or impact with a target with non-uniform resistance to theimpact). In general, the “impact detection and time history sensor”embodiment of FIG. 20 may be designed to detect either only the targetimpacts or both all-fire setback (shock) acceleration as well as targetimpacts.

It is also appreciated by those skilled in the art that the circuitryoutput(s) may be similarly used to provide logic signal flags when atarget impact of one or more prescribed shock levels and durations isencountered, as for example implemented in the low power circuitry ofFIG. 18. Then as shown in the schematic of FIG. 17 and its example ofimplementation in FIG. 18, the circuitry provides logic signal flags forone or multiple target impact shock acceleration levels that can bedirectly read by other devices through digital ports. The use of the andpreviously described logic signal flags, minimal detection electronicsand computational capability are required to be provided in the “poweredoutput level detection and recording unit” of the “impact detection andtime history sensor” of the embodiment of FIG. 20.

The operation of the “safety and all-fire detection circuitry”embodiments of FIGS. 13, 19 and 19A were described for the detection ofprescribed all-fire conditions in terms of the munitions firing setbackacceleration level and its duration. In the “impact detection and timehistory sensor” of the embodiment of FIG. 20, target impact(s) to one ormore prescribed impact shock levels are similarly detected. All other“non-impact” conditions, such as lower level shock loading due toencounters with very light structures or objects and vibration duringthe flight and other similar events and high noise are differentiatedfrom the prescribed impact conditions (usually shock levels anddurations). The “passive all-fire detection sensor” embodiments of FIGS.17 and 18 can also be used as described previously for the detection ofprescribed munitions all-fire setback accelerations level and duration(all-fire condition) and rejection of all aforementioned “no-fire”conditions to detect munitions target impact(s) to one or moreprescribed impact shock levels (thresholds) while differentiating themfrom all other “non-impact”conditions.

In the schematic of the basic embodiment of the “impact detection andtime history sensors” (or alternatively indicated as “void detector” or“void counter”) shown in FIG. 20, as was previously described for the“safety and all-fire detection circuitry” of the embodiment of FIG. 13(or its alternative embodiments of 19 and 19A), when the munitionsequipped with the present “impact detection and time history sensor”impacts a target (here considered to be a significant barrier like abunker wall or the like—with a significant barrier hereinafter definedas those that cause at least the first prescribed impact threshold leveland duration of the “impact detection and time history sensor” to detectit as an impact event), a prescribed impact condition is similarlydetected by the voltage level of the capacitor C1 while the circuitryprevents the charging of the capacitor C1 to the prescribed voltagelevel if the generated piezoelectric charges are due to theaforementioned non-impact conditions (no-fire conditions for the case ofthe for the case of embodiments of FIGS. 13, 19 and 19A) areencountered. Once an impact condition is detected, the provided “poweredoutput level detection and recording unit” of the “impact detection andtime history sensor” shown in FIG. 20 “records” the event and itsrelative time of occurrence. The detection and “recording” capabilitiesof the “impact detection and time history sensors” may be implemented innumerous different schemes and using different electronics componentsand logics circuitry and/or microprocessor most appropriate for theapplication at hand and the device(s) using the generated information.In munitions applications, however, the main issues of concern inaddition to reliability and safety also include low power requirement,volume efficiency (i.e., miniaturization capability), firing setback andharsh environment survivability.

Examples of the implementation of the present “impact detection and timehistory sensors” of the embodiment of FIG. 20 are provided. It will beappreciated by those skilled in the art that the following embodimentsof the present “impact detection and time history sensors” (oralternatively indicated as “void detector” or “void counter”) inventionsare provided only as examples of their possible implementation,particularly for munitions applications, and should not be considered asan intention to exclude other implementations of the sensor design.

In the schematic of the embodiment of FIG. 20, the “powered output leveldetection and recording unit” portion of the “impact detection and timehistory sensor” embodiment is shown enclosed by dashed lines. In thepresent method, the “safety and all-fire detection circuitry” of theembodiment of FIG. 13 (or its alternative embodiments of 19 and 19A) isused as previously described to detect target impact by the munitions inwhich the sensor is mounted and “record” the time history of thedetected impacts. In the embodiment of FIG. 20, the “safety and all-fire(in this case target impact) detection circuitry” (hereinafter alsoreferred to as “safety and target impact detection circuitry”) as isshown to be used to detect two levels of target impact shock levels atOUTPUT1 and OUTPUT2, even though as it was previously described for theembodiment of FIGS. 17 and 18, more than two target impact levels mayalso be similarly made detectable.

In one “impact detection and time history sensor” embodiment, the“safety and target impact detection circuitry” of the embodiment of FIG.20 is used to provide logic signal flags (for example, as was describedfor the embodiment of FIG. 18) for one or multiple target impact shockacceleration levels (in the schematic of FIG. 20 for two target impactshock or the like acceleration levels) that can be directly read by theprocessor unit 30 (or other appropriate logic circuitry or devices)through digital ports as shown in FIG. 21. The processor unit 30 isconsidered to be equipped with input digital ports, appropriately sizedmemory, timing source, etc., that are commonly provided on such signalprocessing units as is well known in the art. As examples, the processorunit 30 may be constructed with CY8C21334-12PVXE from CypressSemiconductor Corporation which has an internal RC clock and that canwork in a wide range of temperatures can be used. For this In FIG. 21,the “powered output level detection and recording unit” portion of thepresent “impact detection and time history sensor” embodiment (see FIG.18) is indicated by dashed lines.

In the schematic of FIG. 21, the indicated outputs OUTPUT 1 and OUTPUT 2are considered to be outputs of the logic level comparators U1 and U2(see the schematic of FIG. 18). The reference voltage (FIG. 18) may beprovided as shown for the embodiment of FIG. 18 or directly from thepower source 31 of the “powered output level detection and recordingunit” as shown in FIG. 20. As a result, when the munitions impacts atarget, when the impact shock acceleration level reaches the prescribedthreshold of the first logic level comparator U1, the OUTPUT1 provides asignal indicating the event (preferably by a logic signal voltage levelappropriate for the detecting device electronics, for example a 3.3V or5V or +/−12V as described for the embodiments of FIGS. 17 and 18).Similarly, if the impact shock acceleration level increased further andreaches the prescribed threshold of the second logic level comparatorU2, the OUTPUT2 would then provide a signal indicating the event. In asimilar manner, if more than two logic level comparators are provided inthe “safety and all-fire detection circuitry” of the embodiment of FIG.20 (as described for the embodiment of FIG. 13 or its alternative ofFIGS. 19 and 19A and the embodiments of FIGS. 17 and 18), eachprescribed impact shock acceleration level that is reached generates asignal indicating the event to the processor unit 30. The processorwould then “record” each event and their relative time.

It will be appreciated by those skilled in the art that as waspreviously described for the embodiments of FIGS. 13-19 and 19A, whenthe when the munitions encounter with a significant barrier ends, i.e.,when the munitions exits the barrier, the piezoelectric voltage drops(to near zero) below the voltage level on C1 and the diode D2 causesessentially all charges accumulated in the capacitor C1 to bedischarged. As a result, the outputs OUTPUT 1 and OUTPUT 2 of all logiclevel comparators U1 and U2 will drop to near zero, indicating to theprocessor unit 30 that the target has been essentially exited (at leastup to its softer portion indicated to be below the threshold of thefirst logic level comparator U1). Similarly, once the impact thresholdlevel falls below the level indicated by the logic level comparator U2,the OUTPUT2 of the comparator drops to near zero, thereby similarlyindicating the event to the processor unit 30.

As an example, if the munitions in which the present “impact detectionand time history sensor” embodiment of FIGS. 20-21 is mounted encounterstwo significant barriers (i.e., barriers that cause at least the firstprescribed impact level and duration of the “impact detection and timehistory sensor” to detect it as an impact event), then the time historyof the detected events may look as shown in the plot of FIG. 22. In theplot of FIG. 22, the munitions 40 is shown in the positions 32, 33 and34, corresponding to its position prior to encountering the significantbarrier 35, after having encountered the significant barrier 35 andprior to encountering the significant barrier 36 and after havingencountered the significant barrier 36, respectively. The top graph ofFIG. 22 is intended to show the output flag activation condition as afunction of time as the munitions 40 travels from its position 32through the significant barrier 35 and then travels through its position33 to the significant barrier 36 and through it to its position 34. Inthe top graph of FIG. 22, the “impact detection and time history sensor”that is mounted in the munitions 40 is considered to experience theimpact with the significant barrier 35 and at the indicated time t₀detect the aforementioned first target impact shock level and therebygenerate an output flag at the OUTPUT1, with the impact shock levelincreasing to the aforementioned second target impact shock level andthereby generating an output flag at the OUTPUT2 at the indicated timet₁. The impact shock level experienced by the munitions 40 is thenconsidered to stay around the aforementioned second impact shock leveluntil the time t₂, at which time the impact shock level drops below thesecond but above the first impact shock level and stays in the sameregion until the time t₃, at which time the impact shock level dropsbelow that of the aforementioned first impact shock level. The munitions40 then travels towards the second significant barrier 36 and at thetime t₄ the “impact detection and time history sensor” is considered todetect the aforementioned first target impact shock level and therebygenerate an output flag at the OUTPUT1 until the time t₅, at which timethe impact shock level drops below that of the aforementioned firstimpact shock level.

In an embodiment, processor unit 30 of the “impact detection and timehistory sensor” embodiment of FIGS. 20-21 is provided with a timingclock, I/O ports and the related components and enough memory capacityto record the events indicated in the top graph of FIG. 22 in terms ofthe generated output flags and their relative times of occurrence t₀-t₅for use for other electrical and electronics units of the munitions.

It will be appreciated by those skilled in the art that theaforementioned time t₀ and t₄ would usually occur slightly after themunitions impact with the significant barriers 35 and 36, respectively,and that the amount of such delays is dependent on the resistance of theencountered significant barrier surfaces and the strengthcharacteristics of the munitions structure, particularly around itsimpacting surfaces to the location of the “impact detection and timehistory sensor” mounting.

A schematic of an alternative embodiment of the “impact detection andtime history sensor” of FIGS. 20 and 21 is shown in the schematic ofFIG. 23. This embodiment employs one of the basic “safety and all-firedetection circuitry” of embodiments of FIG. 13 or 19 or 19A to designsensors for detecting one or more target impact (shock) loading andtheir impact level profiles as a function of time. It will beappreciated by those skilled in the art that as was previouslyindicated, such sensors which are designed to detect (usuallysignificant) barriers, are in fact also detecting (relatively) freespace (or void) between such barriers and can also be referred to as“void detectors” or “void counter”. In the example of basicimplementation of the present embodiment shown in FIG. 23, the voltagesignals from the “safety and all-fire detection circuitry” output(indicated as OUTPUT in the schematic of FIG. 23) and the piezoelectricelement voltage output (indicated as VP in the schematic of FIG. 23) areconnected to the analog-to-digital converter (A/D) inputs of the MCU(micro-controller unit) via voltage followers, which can be implementedwith the Texas Instruments OPA2277 high precision operational amplifieras is well known in the art.

The ground “safety and all-fire detection circuitry” (GND) is connectedto the analog ground of the MCU. It is noticed that the voltagefollowers can also be configured to specific gain with resistors, sothat they scale the voltage to be measured at the OUTPUT of the “safetyand all-fire detection circuitry” as well as the voltage VP of thepiezoelectric element (usually down) to the measurement range of A/Dconverters of the MCU.

The micro-controller unit (MCU) may be of any type appropriate of thespecific application. As an example, we may use a model CY8C28243-24PVXIfrom Cypress Semiconductor Corporation for this purpose. Such a MCUfeatures on-chip RC clock of up to 48 MHz with 2.5% fabricationaccuracy, and is integrated with 16 KB flash memory, 1 KB SRAM memoryand A/D modules (up to 15.6 k sample rate at 6 bit resolution).Additional memory may also be added depending on the selected samplingrates and the total length of time that sampling is desired to becontinued.

In general, a voltage regulator can provide proper voltage source frompower supplier (a battery or capacitor or super-capacitor or the like)to the MCU. The switch SW enables the MCU to start the program. Theswitch can for example be a simple manual on/off switch when the systemis used in the laboratory for testing purposes, or when used inmunitions, it could be an electronic switching device similar to the onedescribed for the embodiment of FIG. 16, which is similarly powered bythe piezoelectric element or could be a latching G-switch that is turnedon by the firing setback acceleration and would stay on followingactivation.

Once the switch SW is closed, the MCU would continuously sample voltagesignals ay A/D 1 and A/D 2, FIG. 23, and store the information as afunction of time in the device internal and external (if provided)memory or is transmitted directly to the host processor (munitionscontrol system processor, which may be the MCU itself) for processing.As a result, essentially continuous time history of impact shock levelsare provided by the device once such impacts with levels above theprescribed levels are detected. For example, considering significantbarrier encounters shown in the schematic of FIG. 22, the MCU ispreferably programmed to ignore the A/D 1 input until it reaches theaforementioned prescribed level indicating an encounter with asignificant barrier (time t₀ in the plot of FIG. 22), and sample/recordor process impact shock levels until the time t₃, when the munitions 32has exited the significant barrier 35. As a result, a nearly continuousprofile of impact shock level, i.e., barrier “strength”, as a functionof time is measured (as compared to the step-wise output shown in theplot of FIG. 22 for the portion of the shock levels between theindicated OUTPUT1 and OUTPUT2). It is also appreciated by those skilledin the art that since the munitions velocity is approximately known orreadily calculated, the impact shock level profile as a function of thebarrier thickness is also approximately determined. The impact shocklevel is similarly measured during the round 32 encounter with thesecond significant barrier 36, FIG. 22.

When a relatively short string of data is to be recorded, a circularbuffer can be formed. Algorithms well known in the art can then be runin the MCU processor to monitor the buffer. Then when the bufferindicates a valid event sequence, for example for the case of munitions,when a prescribed type and number of encounters with previouslydescribed significant barriers are detected, the algorithm would passthe information to the munitions control processor for decision makingpurposes or in testing equipment, would save the data on itsnon-volatile memory.

The rest of the available GPIO (general purpose input/output) bus andanalog (A/D and D/A) bus of the MCU can be used to input/output digitalflags and analog control signals. For example, by using two GPIO pins asSCLK and SDATA, an I2C serial port can be implemented for communicatingwith host processor (if provided) to upload the samples stored in MCU'smemory.

It will be appreciated by those skilled in the art that the “impactdetection and time history sensor” embodiment of FIG. 23 has theadvantage of being capable of providing essentially continuous impactshock level information once the prescribed impact threshold level andduration has been reached. In contrast, the embodiments of FIGS. 20 and21 provide a step-wise, multi-level indication of the impact shock levelinformation. The latter information is usually sufficient in manyapplications. In addition, the embodiments of FIGS. 20 and 21 also havethe advantage of requiring relatively simple electronics to constructwithout the need of MCUs and A/Ds and the like. Thereby these devicesbecome significantly less complex, less costly and faster in response.

It is also appreciated by those skilled in the art that more than one“impact detection and time history sensor” (of either one of theembodiments of FIG. 20, 21 or 23) may be mounted in munitions (e.g.,round 32 shown in FIG. 22) to detect/measure impact shock levels alongthe path of travel of the round (see FIG. 22) as well as in the lateraldirection(s). In a preferred embodiment, at least three such “impactdetection and time history sensors” are used and at least one isoriented to detect/measure impact shock level in the axial direction(i.e., along the path of travel of the round) and at least two are usedto detect/measure impact shock levels in two independent lateraldirections (preferably orthogonal directions). In such configurations,the impact detection and time history sensors are capable of providinginformation as to the direction of target impact and/or the structuralcharacteristics of the impacted and penetrated target.

It is noted that the piezoelectric elements used in the embodiments ofFIGS. 13-21 and 23 are in fact electrical energy generators that convertmechanical energy to electrical energy (charges) that are then used topower the described circuitry and elements. It is also noted that theindicated piezoelectric elements are assemblies containing piezoelectric(preferably stack) elements and in general other elements such as massand spring (elastic) elements that are packaged in a particular mannerto allow them to generate the electrical energy when subjected to aprescribed shock loading direction. In the following, the basic methodsof packaging to construct such piezoelectric-based electrical energygenerators suitable for the present applications are described indetail. It is, however, noted that the provided example of suchpackaging is provided only for describing the disclosed basic methodsand are not intended to limit this disclosure to this particularpackaging configuration.

In one embodiment, the aforementioned piezoelectric-based electricalenergy generator 50 (herein referred to as “piezoelectric element”) ofthe embodiments of FIGS. 13-21 and 23 is packaged as illustratedschematically in FIG. 24. The piezoelectric element 50 is provided witha housing 41, which could for example cylindrically shaped or any othershape that best matches the available space in the device it is beingmounted. At least one piezoelectric (preferably stack) member 42 isfixedly attached to one side of the housing 41 (in the schematic of FIG.24 to the bottom surface of the housing 41 as seen in the illustration).A mass 44 is then positioned above the piezoelectric member 42 togetherwith the spring (elastic) element 43, which separates the mass 44 fromthe piezoelectric member 42 as shown in the schematic of FIG. 24. Thespring element 43 is preferably preloaded in compression so that themass element 44 is normally in contact with the top surface 45 of thehousing 41, even when the subjected to certain level of acceleration inthe direction of the arrow 46.

When the piezoelectric element 50 is used in the embodiments of FIGS.14-16 to initiate pyrotechnic materials via the provided bridge wires asa result of the all-fire setback shock acceleration, or for thedetection of one or more firing setback acceleration (shock) levels aswas described for the embodiments of FIGS. 17 and 18, or for otherfiring setback acceleration (shock) purposes in the “safety and all-firedetection circuitry” embodiments of FIGS. 13, 19 and 19A, then thepiezoelectric element 50 is mounted in the munitions such that it isoriented to experience the firing setback acceleration essentially inthe direction of the arrow 46. The spring element 43 is generallyselected to have relatively high stiffness and preloaded to keep themass 44 in contact with the surface 45 of the housing 41. And if thedevice is subjected to acceleration (shock) loading in the direction ofthe arrow 47 (direction of the firing set-forward acceleration) or inthe lateral directions, then level of forces acting on the piezoelectricmember 42 is minimally changed, thereby the piezoelectric member wouldgenerate minimal charges. However, if the piezoelectric element 50 issubjected to shock loading due to the firing setback in the direction ofthe arrow 46, then the acceleration would act on the inertial of themass 44 and applies a force on the piezoelectric member 42 proportionalto the mass of the mass 44 and the setback acceleration and therebycauses it to generate electrical charges to operate the aforementionedcircuitry.

On the other hand, when the piezoelectric element 50 is used in the“impact detection and time history sensor” embodiments of FIG. 20, 21 or23, then the piezoelectric element 50 is mounted in the munitionsoriented such that it experiences the impact shock acceleration in thedirection of the arrow 46. As a result, the firing setback accelerationwill not generate a significant loading of the piezoelectric member 42and thereby would not generate a significant amount of electricalcharges to activate the “impact detection and time history sensors”.

It will be appreciated by those skilled in the art that theaforementioned methods of designing the disclosed “safety and all-firedetection circuitry” embodiments of FIGS. 13, 19 and 19A; theembodiments of FIGS. 14-16 to initiate pyrotechnic materials via theprovided bridge wires as a result of the all-fire setback shockacceleration; the passive shock detection embodiments of FIGS. 17 and18; and the “impact detection and time history sensor” embodiments ofFIG. 20, 21 or 23 as well as their similar implementations may be usedto for non-munitions, including many industrial as well as commercialapplications.

For example, the passive all-fire setback acceleration (shock) leveldetection sensors of the embodiments of FIGS. 17 and 18 may be used todetect vibration in machinery when its amplitude exceeds a prescribedthreshold and provide input to the system control to take appropriateaction such as reduce power or undergo emergency stop. In a similarmanner, the sensors may be used to detect the start of a process inmachinery and initiate certain processes; for example detect the startof drilling process at the drilling head of an oil or gas drillingequipment and thereby turn-on certain processes such turning on thesensory and control and data acquisition and transmission electronics tominimize power consumption or the like or perform other on/off switchingor flagging action.

Even the embodiments of FIGS. 14-16 to initiate pyrotechnic materialsvia the provided bridge wires as a result of the all-fire setback shockacceleration can be used to initiate pyrotechnics and/or explosives usedto actuate certain Cartridge Actuated Devices (CAD) for emergencyactuation of valves or door/exits or ejection of pilot or initiate otheremergency actions when an explosion or earthquake or other high-shockproducing events have occurred.

It will be appreciated by those skilled in the art that the safety andall-fire detection circuitries of FIGS. 13, 19 and 19A may be used inany of the embodiments of FIGS. 14-18, 20 and 23 depending on theapplication.

It is also appreciated by those skilled in the art that implementationsother that the circuitry shown in the schematics of FIGS. 13-21 and 23for the disclosed methods are also possible for achieving essentiallythe same functionalities. As such, the disclosed implementations of thedisclosed methods as shown in the schematics of FIGS. 13-23 are toprovide examples of their preferred embodiments and are not intended tolimit their implementations only to the disclosed implementations.

It is also appreciated by those skilled in the art that as was describedfor previous embodiments, a magnet and coil generator 20 that forms avibrating mass-spring system shown in the schematic of FIG. 12 may besimilarly used in place of or in addition to the piezoelectric elementsof the embodiments of FIGS. 13-20 and 23.

A stand-alone piezoelectric (usually in stack form) element can bemodeled as a capacitor C_(p) connected in parallel to a charge source Qas shown in FIG. 25A. The charge source Q generates charge proportionalto the axial (normal) strain of the piezoelectric element as it issubjected to axial (normal) loading, and thereby sends the charge ascurrent i to the capacitor C_(p) of the piezoelectric element. Thecharges accumulated on the capacitor C_(p) produces a voltage V, whichis the so-called open circuit voltage of the piezoelectric element. Whenthe piezoelectric element is connected to another circuitry, thegenerated charge and current are the same, but due to the resultingcharge exchange with the other circuitry, the in circuit voltage of thepiezoelectric element may be different from the open circuit voltage V.

A typical plot of the profile of the charge level on the piezoelectricelement (FIG. 25A) as it is subjected to a short duration impact loadingas a function of time is shown in FIG. 25B. The maximum amount ofcharges Q (in Coulomb) is dependent on the size of the piezoelectricelement and the applied impact force levels. In most cases of interest,the impact loading duration may be as low as 10-100 microseconds.

It will be appreciated by those skilled in the art that when harvestingelectrical energy from shock loading impact or other similar very shortduration “pulsed” loading, the mechanical to electrical energyconverting elements such as piezoelectric elements or magnet and coilelements used for this purpose are subjected to very short duration“pulsed” excitation. Currently used electrical energy collection andcapacitor storage methods are, however, extremely inefficient when the“pulse” duration is very short and sometimes in the order of tens ofmicroseconds or even less. Methods and devices are therefore highlydesirable for efficient harvesting the electrical energy that isgenerated by electrical energy generators such as piezoelectric elementsor magnet and coil elements when subjected to such very short duration“pulsed” loading.

The method and devices of providing a highly efficient energy harvestingdevice is shown in the basic circuitry of the embodiment of FIG. 26.Here the circuitry of FIG. 26 and its operation is described for thevery short duration charges that are generated by a piezoelectricelement when it is subjected to very short duration loading, such asthose experienced as a result of very short duration impact loading. Inaddition, in the circuitry of FIG. 26 only the very basic elements thatare needed for its proper operation are shown. But it will beappreciated by those skilled in the art that a user may add otherelements to adapt this circuitry to many other specific applications athand.

The novel very short duration pulse energy harvesting circuitry of theembodiment of FIG. 26 harvests energy from short duration chargesgenerated by the device piezoelectric element (indicated in short aspiezo in FIG. 26) in two distinct stage. In the first stage, theelectrical energy (charges) generated by the piezoelectric element dueto the very short duration impact loading (a transient pulse) is storedin the piezoelectric element (acting as an electrical energy storagecapacitor). In the second stage, the electrical energy stored in thepiezoelectric element is transferred to the energy harvestercapacitor(s).

The basic energy harvesting circuitry for very short duration loading ofpiezoelectric elements shown in FIG. 26 may be divided into twosub-circuits “A” and “B” as indicated by dashed lines in FIG. 26. As canbe seen in FIG. 26, the sub-circuit “A” includes the inductor L1, diodeD1 and the piezoelectric element. This circuit and without the diode D1would form an LC resonant circuitry, and its resonance frequency isselected based on the range of the duration of the piezoelectric loadingas seen in FIG. 25B, with the period of the resonant frequency beingpreferably around 0.5 to 1.5 times the maximum duration of thepiezoelectric element loading (indicated by the duration of the chargein FIG. 25B).

The inductor L2 and capacitor C of the sub-circuit “B” form another LCcircuitry (without the diodes D3) with the natural frequency, which isselected to be significantly lower than that of the natural frequency ofthe sub-circuit “A”. As a result, during the aforementioned very shortduration loading of the piezoelectric element, FIG. 26, which wouldresult in a very short duration generated charge pulse of the type shownFIG. 25B, only the sub-circuit “A” of the device (FIG. 26) would providea significant response to the generated “pulsed” charge. That is, duringthe short duration of the generated “pulsed” charge, FIG. 25B, theeffects of the presence of the sub-circuit “B” can be neglected.

The sub-circuit “A”, FIG. 26, with the piezoelectric element model ofFIG. 25A is shown in FIG. 27. As was previously described, as thepiezoelectric element of this circuitry is subjected to a very shortduration loading, it would produce charges essentially proportional tothe level of subjected loading, a typical such charge level profilehaving been illustrated in the plot of FIG. 25B. Here, as the chargesbuild up on the piezoelectric element due to the applied short durationloading, as indicated in FIG. 27, a current i₁ is generated by thepiezoelectric equivalent charge source Q; resulting in a current i2passing through the inductor L1; and a current i3 that would result incharging (or discharging) the equivalent capacitor C_(p) of thepiezoelectric element, with the relationship i₁=i₂+i₃ having to besatisfied at all times. In the circuit diagram of FIG. 27, V_(p) is thecircuit voltage of the piezoelectric element.

As an example, consider the case in which the period of the naturalfrequency of oscillation of the LC circuit formed by the inductor L1 andthe equivalent capacitor C_(p) is 75% of the impact duration T (FIG.25B). The resulting currents i₁, i₂, and i₃ during the impact would thenhave typical profiles as shown in the plot of FIG. 28. FIG. 29 is theplots of the corresponding profiles of the voltage V_(p) for the opencircuit case, i.e., for the piezoelectric element alone as shown withits equivalent circuit in FIG. 25A (dashed line) and in circuit (FIG.27) voltage during the short duration impact loading of thepiezoelectric element (solid line).

At the beginning of the process of short duration impact loading of thepiezoelectric element (FIG. 26), the charges generated by thepiezoelectric element produces a current i₁, FIG. 27. The current i₁will then branches into the current i₂ and i₃ as shown in FIG. 28. Thepositive current i₃ begins to accumulate charges on the piezoelectricequivalent capacitor C_(p), thereby the voltage V_(p) begins toincrease. The current i₂ cannot increase instantly due to the presenceof the inductor L1, which limits the change of current to stayproportional to the voltage across the inductor. Thus, the electricalenergy generated by the piezoelectric element loading due to thegenerated charges is transferred to the inductor L1 and the capacitorC_(p). The energy stored in the capacitor C_(p) being proportional tothe square of the voltage V_(p), and the energy stored in the inductorL1 being proportional to the square of the current i₂.

During the process of short duration impact loading of the piezoelectricelement (FIG. 26), at certain time t₁, the inductor current i₂ catchesup with the current i₁, and since the voltage V_(p) is still positive,i₂ would still keep on increasing, FIGS. 27 and 28. At this point, thecurrent i₁ is generally still positive but decreasing. Therefore, at thetime t1, the current i₃ becomes zero and begins to flow in the oppositedirection, i.e., becoming negative, FIG. 28. During the process of shortduration impact loading of the piezoelectric element, the (circuit)voltage V_(p) of the piezoelectric element (FIG. 27) will vary as shownwith solid line in the plot of FIG. 29. As can be seen in the plot ofFIG. 29, as long as the current i₃ is positive, the capacitor C_(p) ischarged, thereby at the time t₁ when the current i₃ becomes zero andbegins to become negative, the voltage V_(p) reaches its positive peaklevel. From that point on, since the current i₃ is always negativeduring the remaining of the short duration impact loading of thepiezoelectric element, the current i₃ keep on negatively charge thecapacitor C_(p). The voltage V_(p) would thereby begin to decrease asshown in FIG. 29 until it becomes zero at the time t₃. It is noted thatafter the time t₁, the electrical energy generated by the piezoelectricelement as well as the electrical energy stored in the capacitor C_(p)begin to be transferred to inductor L1.

At the time t₂, FIGS. 28 and 29, the piezoelectric element hasexperienced its peak loading, thereby generating its maximum opencircuit voltage (FIG. 29) and charges (FIG. 25B). From this point on,the piezoelectric element will begin to absorb charges, and the currenti₁ would therefore change direction and becomes negative as shown inFIG. 28. Noting that since the voltage V_(p) is still positive at thistime, i.e., at time t₂, the current i₂ is still positive and increasing.As a result, from the time t₂, the current i₁ continues to become morenegative (i.e., the flow of the current i₁ increases in oppositedirection of that shown in FIG. 27) and will generally cause the currenti₃ to keep on becoming more negative due to the flattening of the levelof the current i₂, FIG. 28, thereby continuing to decrease the voltageV_(p), FIG. 29. From the time t₂ and as long as the voltage V_(p) isstill positive, part of the energy stored in the capacitor C_(p) isbeing transferred to the inductor L1 while part of the energy (chargesstored in the capacitor C_(p)) is returned back to the piezoelectricelement.

At time t₃, the voltage V_(p) reduces to zero while the current i₂reaches its maximum and the current i₃ keeps its negative trend. Theenergy stored in the inductor L1 will also reach its maximum and thecharges in the capacitor C_(p) are fully discharged. At this time t₃,the capacitor C_(p) is ready to collect negative charges. The currentsi₁ and i₂ are combined and begin to negatively charge the capacitorC_(p), until the time t₄, when all the energy in the inductor L1 hasbeen transferred to the capacitor C_(p), FIG. 28. At this time, i.e., atthe time t₄, the current i₂ becomes zero, FIG. 28, and would generallytends to go negative and draw energy from capacitor C_(p). However, thepresence of the diode D1, FIG. 27, prevents the return current. As aresult, from this time (t₄) on, the inductor L1 is effectivelydisconnected from the circuitry and the charge source Q (FIG. 27)produces negative current i₁=i₃, and keeps on accumulating negativecharges on the capacitor C_(p) until the short duration impact ends atthe time T.

As can be seen from the voltage plots of FIG. 29, the open circuitvoltage (dashed line) and in circuit voltage V_(p) of the piezoelectricelement has the same profile as the generated charge Q shown in the plotof 25B since they are proportional to each other. The in circuit voltage(solid line in FIG. 29) however reaches its positive maximum very earlyon at time t₁, when the current i₃ becomes zero (FIG. 28). After thetime t₁ the current i₃ is always negative, and hence the in circuitvoltage keeps dropping until the end of impact loading, i.e., at time T.It will be appreciated by those skilled in the art that that the areaunder the i₃ curve corresponds to the amount of charges that are finallystored in the equivalent capacitor C_(p) of the piezoelectric elementand that the final in circuit voltage is higher than the maximum opencircuit voltage.

It will be appreciated by those skilled in the art that in the aboveexample, all components of the provided circuitry are considered to beideal and linearly behaving. In addition, the piezoelectric element isconsidered to produce charges proportional to the applied short durationimpact loading, i.e., its own dynamic behavior is also neglected. Theseassumptions are obviously not totally true and the described response ofa real system is expected to vary slightly from its idealized model. Forexample, inductors usually also provide certain amount of resistive loadand the equivalent capacitance C_(p) of the piezoelectric element wouldalso exhibit leakage. However, the above idealized model (FIG. 27) stilldoes clearly show the disclosed novel method of harvesting a very highpercentage of the total charges generated by a piezoelectric elementwhen it is subjected to very short duration pulses, which is notpossible to achieve by any of the currently available methods of energyharvesting from piezoelectric elements when subjected to short duration(usually related to impact or other similar type of) loading.

It will also be appreciated by those skilled in the art that neglectingcommonly encountered losses in actual components such as those mentionedabove, at the end of the imparted very short duration (usually impacttype) loading of the piezoelectric element, FIGS. 26 and 27, theabsolute value of the final (negative) voltage V_(p) of the equivalentcapacitor C_(p) of the piezoelectric element will be significantlyhigher than the maximum open circuit voltage that can be achieved. Thisis obviously the case with the present novel circuitry since the chargesgenerated during loading portion of the loading cycle (during which thepiezoelectric element is subjected to increasing compressive loading) issummed up with the charges being “returned” to the piezoelectric elementduring the unloading portion of the loading cycle (during which theapplied compressive load on the piezoelectric element is reduced to zeroby the end of the loading cycle). In fact, if we neglect all losses, atthe end of the short duration impact loading of the piezoelectricelement, the final amount of charges stored on the equivalent capacitorC_(p) of the piezoelectric element is equal to twice the peak value ofcharges generated by the piezoelectric element at its peak loading,i.e., the present novel circuitry can theoretically deliver 100% energyharvesting efficiency.

In the present disclosure, the short duration loading of piezoelectricelements are indicated mostly as those resulting from impact type ofloading. This is usually the case since impact type of loading betweenrelatively stiff objects would generate such short duration compressivestresses. It is, however, appreciated by those skilled in the art thatany other mechanism by which very short duration loading is imparted onthe energy harvesting piezoelectric elements can also use the disclosednovel method highly efficient charge collection and storage. In general,the duration of the shock is considered to be short and in the order oftens or at most hundreds of microseconds since such very short durationcharges is very difficult to collect and store using currently availablemethods. In addition, with very short duration loading (generated charge“pulses”), the required inductor L1 (FIGS. 26 and 27) are relativelysmall.

It is also appreciated by those skilled in the art that the reason foronly considering compressive loading during short duration axial(normal) loading of the piezoelectric elements is the fact that due totheir brittle nature, piezoelectric elements can only be subjected torelatively small tensile stresses. Thereby, for energy harvestingpurposes in particular, piezoelectric elements should be designed to besubjected to compressive loading to maximize the level of stresses(strains) that they are subjected to and thereby have them generatetheir maximum amount of electrical charges. It is, however, appreciatedby those skilled in the art that properly poles piezoelectric elementsmay also be used in energy harvesting devices that subject them to othermodes of stresses such as in shear. In any case, the novel method ofharvesting the generated charges (electrical energy) can still be usedto collect the generated electrical charges for storage in capacitors orfor other direct usage.

At the completion of the short duration (usually impact) loading of thepiezoelectric element, FIG. 26, the generated charges were shown to bestored in the equivalent capacitor C_(p) of the piezoelectric element,FIGS. 25A and 27. The function of the sub-circuit “B” of device of FIG.26 is to transfer the stored electrical energy to the device storagecapacitor C.

In the sub-circuit “B” of the energy harvesting device of FIG. 26, theinductor L2, diodes D2 and D3 and the capacitor C make a capacitanceenergy transfer circuitry to harvest the energy stored in the equivalentcapacitor C_(p) of the piezoelectric element, FIGS. 25A and 27. As waspreviously noted, the natural frequency of the sub-circuit “B” (withoutthe diodes D2 and D3) is considered to be significantly lower than thatof the sub-circuit “A” (without the diode D1), therefore the sub-circuit“B” would have negligible influence on the aforementioned process ofstoring charges (electrical energy) generated by the piezoelectricelement as it is subjected to a very short duration loading to itsequivalent capacitor C_(p). Thus, after the completion of the very shortduration impact loading of the piezoelectric element, the chargesaccumulated in the equivalent capacitor C_(p) of the piezoelectricelement can with relatively high accuracy be considered as a “step”input for this sub-circuit “B” of the energy harvesting device of FIG.26.

With the step input, the energy is transferred to the capacitor C andinductor L2, FIG. 26, from the equivalent capacitor C_(p) of thepiezoelectric element, FIG. 27. When the equivalent capacitor C_(p) hasdischarges essentially all its charges, the diode D2 prevent the energyto be transferred back to the piezoelectric equivalent capacitor C_(p).The diode D3 allows for the transfer of the energy stored in theinductor L2 to capacitor C. However, when essentially no more energy isleft in the inductor L2, the diode D3 prevents the flow of energy fromthe capacitor C back to the inductor L2. As a result, assuming idealcomponents, theoretically all the energy stored in the equivalentcapacitor C_(p) of the piezoelectric element can be transferred to thedevice storage capacitor C. It will be appreciated by those skilled inthe art that when using commonly available components, depending ontheir actual characteristics, for example, resistances in the deviceinductors and leakage in the capacitors, etc., the actual energytransfer efficiency as well as the overall efficiency of the energyharvesting device of FIG. 26 will be less than their ideal levels.

The process described above for the basic circuitry of the piezoelectricbased energy harvesting device was for harvesting the electrical energythat is generated by the piezoelectric element of the device when it issubjected to a very short duration impact type loading and transferringit to a storage capacitor C, FIG. 26, or for using it directly in anelectrical or electronic circuitry. It is, however, appreciated by thoseskilled in the art that once the generated electrical energy istransferred to the storage capacitor C, the piezoelectric element of thedevice may be subjected to a series of short duration impact typeloadings to generate more electrical energy and transfer to the devicecapacitor C. In the meantime, the electrical energy stored in thestorage capacitor C can be used to drive any other electrical orelectronic device or charge rechargeable batteries or capacitors or usedfor any other similar usage. The only requirement is that the shortduration charges should be separated enough in time to allow the chargesstored in the equivalent capacitor C_(p) of the piezoelectric element,FIGS. 25A and 27, to be essentially transferred to the storage capacitorC. The required time interval between consecutive short duration impactloadings of the piezoelectric element is generally about half the periodof the natural oscillation of the LC circuit (inductor L2 and capacitorC) of the sub-circuit “B” of FIG. 26.

It will be appreciated by those skilled in the art that the voltagegenerated by the compressively loading a piezoelectric element increases(mostly linearly) with the increased level of loading. The electricalenergy available in for harvesting is also proportional to the square ofthe generated voltage. It is therefore highly desirable to achieve ashigh a voltage as possible in compressive loading of piezoelectricelements to make larger amounts of electrical energy available forharvesting. In certain applications such as in munitions piezoelectricelements where electrical energy is intended to be generated duringfiring setback acceleration of the munitions or during target impact aswere previously described, then the piezoelectric element is subjectedto only a single shock loading. In such applications, it is highlydesirable to subject the energy harvesting piezoelectric element to avery high compressive loading. However, since the level of compressiveloading at which each individual piezoelectric element would fail (bedamaged, crushed, broken, fractured or the like) is not exactly known apriori, it is highly desirable to develop a method and means ofeffectively harvesting electrical energy by high levels of compressiveloading that could even cause its complete structural failure. As aresult, maximum voltage and therefore electrical energy can be providedby the piezoelectric element for harvesting. Such a method and means aredescribed below.

It will be appreciated by those skilled in the art that when apiezoelectric element is subjected to the aforementioned compressiveloading that could be well above its compressive strength, then thepiezoelectric element would fail in one of its possible modes offailure, for example, it could be crushed considering the brittle natureof most piezoelectric (ceramic) elements, or fail in shear or othersimilar modes. As a result of one of the modes of failures, thepiezoelectric equivalent capacitor C_(p), FIG. 25A, may be shorted(closed) or opened (disconnected from the circuit, FIGS. 25A, 26 and27). However, as it was mentioned previously, since the level ofcompressive loading at which each individual piezoelectric element wouldfail and its mode of failure is not exactly known a priori and alsosince for each mode of failure the result may either be an open or shortsaid circuit equivalent capacitor C_(p), therefore it is highlydesirable to develop a method and means of effectively harvestingelectrical energy that is independent of the mode structural failure ofthe piezoelectric element as well as whether the final state ofpiezoelectric element equivalent capacitor C_(p) is a short or opencircuitry.

It will be appreciated by those skilled in the art that due to thebrittleness of most piezoelectric elements, they can withstand only afraction of their compressive loading in tension. For this reason, mostpiezoelectric based energy harvesting devices are designed to subjecttheir piezoelectric elements essentially in compression. The presentmethods and means of harvesting electrical energy by their high level ofloading that can cause their structural failure is therefore describedfor their compressive loading. The same methods and means can besimilarly be utilized to harvest electrical energy from piezoelectricelements when they are subjected to tensile loading that can cause themto structurally fail.

In general, the present one-time-use energy harvesting devices using thepresent methods and means of harvesting electrical energy from highlevels of loading of piezoelectric elements are of interest in munitionsfor harvesting electrical energy during the firing setback and/or duringtarget impact. The present effectively one-time-use energy harvestingdevices may also be of interest in machinery or other structures forpowering sensors or the like (or even to act as sensors) for detectingfailure or other emergency conditions and transmitting appropriatesignals to the machine controls or operators or to appropriatemonitoring systems for taking appropriate measures to minimize damage tothe affected machinery or perform maintenance or service and the like toprevent a chain of failures in structures or the like. In any case, suchevents are expected to occur very rapidly and are thereby so assumed inthe following embodiments.

The basic circuitry of a piezoelectric-based energy harvesting deviceembodiment for harvesting electrical energy when the devicepiezoelectric element is subjected to high compressive loads that couldcause its structure to fail is shown in FIG. 30. As was previouslydescribed, the stand-alone piezoelectric (usually in stack form) elementof this device can also be modeled as a capacitor C_(p) connected inparallel to a charge source Q as shown in FIG. 25A, and the elementwould also function as was described for the model of FIG. 25A.

The energy harvesting device described by the circuit diagram of FIG. 30also operates in two stages as will be described in more detail. In thefirst stage, the energy generated by the piezoelectric element uponbeing subjected to rapidly increasing compressive loading such as thosethat would be experienced during firing setback or (target) impact orother similar events is partly stored in the inductor L due to thegenerated current pulse and partly in the storage capacitor C_(s), FIG.30. In the second stage, the energy stored in the inductor L is alsotransferred to the storage capacitor C_(s).

A typical plot of the charges generated by a piezoelectric element as afunction of time when subjected to a rapidly applied compressive loadingis shown in FIG. 31. In this plot, the applied compressive load isconsidered to be rapidly increasing until at a time T the piezoelectricelement fails (breaks, is crushed, or the like), when the as a result ofsaid structural failure, the piezoelectric equivalent capacitor C_(p),FIG. 25A, may be shorted (closed) or opened (disconnected from thecircuit, FIGS. 25A, 26, 27 and 32). In the plot of FIG. 31, theessentially vertical voltage drop at the time T indicates that after thefailure event, the charges generated by the piezoelectric element are nolonger available for harvesting.

In the aforementioned first stage, the piezoelectric element is beingsubjected to rapidly increasing compressive loading and would generateincreasing amounts of charges as shown in the plot of FIG. 31. Duringthis time period, since the voltage V_(p) is always positive, the diodeD1 can be treated as open loop and the diode D2 can be treated as aclose loop since the current flow is always in the direction of theinductor L towards and through the capacitor C_(s), FIG. 30. As a resultduring the time period, the circuitry of FIG. 30 functions as itsequivalent circuitry shown in FIG. 32. During this stage, the energygenerated by the piezoelectric element as it is being subjected torapidly increasing compressive loading such as those that would beexperienced during firing setback or (target) impact or other similarevents is partly stored in the inductor L due to the generated current(pulse) and is partly stored in the storage capacitor C_(s), FIG. 32.

At the time T, FIG. 31, the piezoelectric element is considered to failstructurally, and as it was described previously, depending on the modeof failure experienced and final state of the piezoelectric element, thepiezoelectric equivalent capacitor C_(p), FIG. 25A, may be shorted(closed) or opened (disconnected from the circuit, FIGS. 25A, 26 and27). Thus, from the time T, i.e., after the piezoelectric element hasstructurally failed, the piezoelectric element may be modeled as aswitch in the device circuitry of FIG. 30 as shown in FIG. 33, in whichit is also indicated by the numeral 60. The switch 60 may, however, beeither open or closed as it was described depending on its mode offailure and its actual construction and it final state and the like (inFIG. 33 it is shown as being open). As can be seen in FIG. 33, once thepiezoelectric element has failed, the diodes D1 and D2 must beconsidered present in the circuitry and function as will be describedbelow, noting that the diode D2 forces the current i₂ to stay positiveor be zero and that diode D1 will be connected in parallel to the failedpiezoelectric element (and its equivalent switch 60), as a result thecurrent i₂ can still flow either through the diode D1 (when the switch60 is open) or both the diode D1 and the switch 60 when the switch 60 isclosed. Thus, the status (open or closed) of the switch 60 will notaffect the operation of this circuitry as is described below.

In general and to achieve high energy harvesting efficiency, the periodof oscillation of the LC_(s) circuit (without the diodes D1 and D2) mustbe at least twice the impact time duration T. In addition, since thepiezoelectric element can produce high voltage levels at theaforementioned compressive load levels (sometimes well over 200 Volts),therefore the capacitance of the storage capacitor C_(s) must besignificantly higher than that of the equivalent piezoelectric elementcapacitance C_(p).

The operation of the basic circuitry of the energy harvesting deviceshown in the circuit diagram of FIG. 30 during its aforementioned twostages can be described as follows. As the process of compressiveloading of the piezoelectric element begins, the charges generated byits compressive loading produces current the i₁, FIG. 32, which wouldbranch into the currents i₂ and i₃. The (positive) current i₃ will thenbegin to accumulate charges in the equivalent piezoelectric elementcapacitor C_(p), thereby causing the voltage V_(p) to keep to increase.The current i₂ cannot increase instantly in response to the current i₁due to the presence of the inductor L which limits the rate of change inthe current passing through it (i.e., the current i₂) and keeps itproportional to the voltage across the inductor L. Thereby the energygenerated by the piezoelectric element during this period is transferredto the inductor L as well as the capacitors C_(p) and C_(s). Here theenergy stored in the capacitor C_(p) is proportional to the square ofthe voltage V_(p), and the energy stored in the inductor L isproportional to the square of the current i₂.

The general current and voltage profiles when an energy harvestingdevice with basic circuitry shown in FIG. 30 is subjected to rapidlyincreasing compressive loading until its structural failure as waspreviously described are shown in the plots of FIGS. 34 and 35,respectively. In this example, the period of oscillation of the LC,circuit (without the diodes D1 and D2) is considered to be twice theimpact time duration T and the capacitance of the storage capacitorC_(s) is considered to be 20 times that of the capacitance of theequivalent piezoelectric element capacitor C_(p).

During the time period up to the failure of the piezoelectric element attime T, the open circuit voltage V_(p) of the piezoelectric element andthe stored voltage on the storage capacitor V_(s) would have the typicalprofile shown in FIG. 35, noting that since the capacitance of thestorage capacitor C_(s) is considered to be significantly higher (inthis case about 20 times higher) than the capacitance of the equivalentpiezoelectric capacitor, the storage capacitor voltage V_(s) will besignificantly lower than lower than that of the open and closed circuitvoltage V_(p) of the equivalent piezoelectric element capacitor C_(p).

As can be observed in the plots of FIGS. 34 and 35, at a time t1 (beforethe piezoelectric element time of failure T), the inductor current i₂catches up with the piezoelectric current i₁, and since the voltageV_(p)−V_(s) (FIGS. 32 and 35) is still positive, therefore the currenti₂ will still keep on increasing after the time t1. Therefore at thetime t1, the current i₃ becomes zero and begins to become negative,i.e., the equivalent piezoelectric capacitor C_(p) begins to dischargeinto the inductor L. At the time t1, the in circuit voltage V_(p) on thepiezoelectric element also reaches its positive maximum. From the timet1, since the current i₃ becomes negative, i.e., since the equivalentpiezoelectric capacitor C_(p) begins to discharge, the in circuitvoltage V_(p) of the capacitor C_(p) begins to decrease. After the timet1 and until the time of piezoelectric failure T, the energy generatedby the piezoelectric element and the energy stored in the equivalentpiezoelectric capacitor C_(p) are transferred to inductor L and thestorage capacitor C_(s).

At the time T the piezoelectric element is considered to have beenstructurally failed (i.e., crushed or fractured or the like), therebythe remaining electrical energy that is stored in the equivalentpiezoelectric capacitor C_(p) is no longer available and the chargesource is no longer generating any electrical energy. Such a state ofthe piezoelectric-based energy harvesting device of FIGS. 30 and 32 isshown in the schematic circuit of FIG. 33, with the failed piezoelectricelement illustrated as the switch 60 which has been suddenly opened atthe time T. As a result, the current i₂ can only flow in the directionof charging the storage capacitor C_(s), FIG. 33. At this time, thevoltage across the inductor L suddenly changes from V_(p)−V_(s) to−V_(s) by the failure of the piezoelectric element (as V_(p) is suddenlydropped to zero), and the energy stored in the inductor L continues tobe transferred to the capacitor C_(s) until the current i₂ drops tozero. The diodes D1 and D2 are seen to shut the current loop off whenall the inductor L energy is transferred to the storage capacitor C_(s),and prevent the electrical energy stored in the storage capacitor C_(s)from being discharged. In this example used to get the plots of FIGS. 34and 35, the energy harvesting efficiency (indicating the percentage ofelectrical energy that has become available for harvesting that istransferred to the storage capacitor C_(s)) was found to be around 48%.As expected, the final voltage V_(s) of the storage capacitor Cs is seenin FIG. 35 to be lower than open circuit voltage V_(p) of thepiezoelectric element since the capacitance of the capacitor C_(s) wasconsidered to be 20 times higher than that of the equivalentpiezoelectric capacitor C_(p).

It is also appreciated by those skilled in the art that once thepiezoelectric element of the above energy harvesting device, FIG. 30,has structurally failed, the circuit across the piezoelectric elementmay end up to be either open (as shown by the open switch 60 of FIG.33), or may result in shorting the diode D1, which could be indicated asa closed switch 60. In either case, the current i₂ that is flowingthrough the inductor L to charge the storage capacitor C_(p) will passthrough the diode D1 (when the switch 60 is open) or through the diodeD1 and the switch 60 (when the switch 60 is closed). As a result, abovestate of the structurally failed piezoelectric element would essentiallynot affect the energy harvesting efficiency of the present energyharvesting embodiment.

In many applications, an object is subjected to one or of a series ofrelatively short duration shock loadings that may be separated byrelatively very short time intervals. It is noted that hereinafter, ashock loading event is referred to those events in which an object issubjected to a rapidly increasing loading followed by a similarlyrapidly dropping of the loading level, essentially to the pre-shockloading levels, such as those experienced by munitions during the firingor as they encounter and travel through significant barriers as shownschematically in FIG. 22. It is also appreciated by those skilled in theart that such shock loadings are also routinely assumed to be properlyrepresentable by the so-called half sine loading (or acceleration)profile similar to the plot of charges as a function of time shown inFIG. 25B. This is for example the case when an object is impacted by oneor multiple objects traveling at relatively high speed or if an objecttraveling at relatively high speed impacts one or multiple objects orimpacts one or multiple barriers that are positioned at relatively closedistances. The latter condition is experienced for example by munitionsimpacting one or multiple barriers of relatively significant strengththat are positioned relatively close to each other. In such cases, themain shortcoming of currently available sensors such as different typesof available accelerometers is that when such barriers induce relativelylarge shock loading, then before the vibration and other shock loadinginduced and generally oscillatory outputs from the sensor has been“damped” out, the next shock loading may occur. As a result, it becomesextremely difficult, and in many cases, impossible to isolate the sensorresponse from subsequent shock loading events. For example, themunitions may experience multiple shock loadings of tens of thousands ofG that may last 5-10 milliseconds or less and be as little as 5-10milliseconds or less apart.

To provide sensors for detecting and measuring profiles of multipleshock loadings that an object such as munitions may encounter and occurvery short times apart, methods for designing such miniature sensors andtheir electronics and the resulting sensory systems must be provided. Toachieve this goal, methods and related sensory systems must be providedwith the means to minimize the amount of time that it would take thesensory system, including its sensory element, e.g., the piezoelectricelement(s), and its structural elements and electronic circuitry wouldtake to dissipate oscillatory mechanical and electrical energy impartedon the sensory system as a result of each shock loading event. That is,following each shock loading event, the oscillatory mechanical andelectrical energy, hereinafter referred to as “residual energy”, that ispassed to the various elements of the sensory system must besubstantially dissipated so that the corresponding output level of thesensory system (effectively sensory noise level) is reduced enough toallow for the detection and measurement of the profile of next shockprofile with the required precision.

It will be appreciated by those skilled in the art that theaforementioned mostly oscillatory mechanical and electrical energyimparted to the sensory system (residual energy) are mainly in the formof mechanical vibration energy due to the structural flexibility of thevarious components of the sensory system and as residual electricalcharges in the piezoelectric element. The residual electrical chargesremaining in the sensor piezoelectric element(s) following a shockloading is readily seen to be mainly due to the leakage and dissipationof the charges in related electrical energy consuming elements of thesensor. This occurs since the piezoelectric element(s) and the relatedelectrical and electronic elements to which it is connected consumecertain amount of electrical charges during the shock loading andunloading cycle (hereinafter and for the sake of simplicity, thepiezoelectric element(s) are considered to be subjected to purecompressive loading—particularly since piezoelectric elements arecommonly used in compression and generally preloaded to ensure that theyare not subjected to tensile stresses during the loading cycle since thepiezoelectric materials commonly used are highly brittle and cannotresist a significant amount of tensile stresses). Then following the(compressive) shock loading that is considered to generate positivecharges on the piezoelectric element, and not considering the vibratoryoscillations, the piezoelectric element(s) will tend to returnessentially to its initial (unstrained) length, thereby the equivalentof the aforementioned dissipated charges will be generated andaccumulated on the piezoelectric element as negative charges (oppositeto the positive charges generated as the result of the compressive shockloading of the piezoelectric element(s)). This residual negativeaccumulated charges, if not dissipated rapidly, would reduce the levelof the total amount of charges that will be generated during the nextshock loading cycle, thereby negatively affecting the accuracy withwhich subsequent shock loading events can be detected and measured.

In the following embodiments, methods to dissipate the aforementionedresidual energies in the present sensors for detecting and measuringprofiles of multiple shock loadings that an object such as munitions mayencounter and occur very short times apart and related sensory systemsare disclosed. The presented methods and resulting sensory systems donot require external power to suppress the residual energies followingeach shock loading event, i.e., they are totally passive. However,methods to dissipate the aforementioned residual energies as well asresulting sensory systems that use external power sources to increasethe effectiveness of the sensory system is also provided. An advantageof passive sensory systems is that even though their effectiveness maybe relatively less than externally powered (“active”) systems in certainapplications and for certain shock loading profiles, their operation isalways fully stable.

In the following embodiments, in addition to methods to dissipate theaforementioned residual energies in the present sensors for detectingand measuring profiles of multiple shock loadings that an object such asmunitions may encounter and occur very short times apart and relatedsensory systems, methods and related devices to minimize the response ofthe sensory system to structural vibration and so-called ringing (stresswave induced) reaction of the object to which the present sensory systemis attached are also provided. The disclosed methods and devices includethose that are fully passive, i.e., do not require external sources ofelectrical energy, as well as those that utilize externally providedelectrical energy.

The piezoelectric element of a typical shock loading detection andmeasurement may be packaged as shown in the schematic of FIG. 36 andindicated by the numeral 100. The piezoelectric element package 100 isprovided with a housing 101, which could for example be cylindricallyshaped or have any other shape that best matches the available space inthe device in which it is being mounted. At least one piezoelectricmember 102, which can be stack of piezoelectric members, is fixedlyattached to one side of the housing 101 as shown in FIG. 36, i.e., inthis case to the bottom surface of the housing 101. A mass 103 ofappropriate size which can cover the surface of the piezoelectricelement 102 is also generally fixedly attached to the other side of thepiezoelectric element as shown in FIG. 36. The inertia (mass) of themass element 103 is dependent on the maximum level of shock loading tobe detected and measured and the material and structural characteristicsof the piezoelectric element to withstand the shock loading levels andto retain its piezoelectric characteristics. It will be appreciated bythose skilled in the art that for cases of low shock loading levels,larger mass elements 103 are to be used for the sensor to providedetectable levels of output (generated charge voltages). In certainapplications in which the levels of shock loading is relatively high,the sensor may not require to be provided with a separate mass element103 and the inertia (mass) of the piezoelectric element 102 may beenough to generate the detectable output signal. A compressivelypreloaded spring (elastic) element 104 is also positioned between theinterior surface 105 of the housing 101 and the mass element 103 toensure that as the package 100 of the sensor is subjected toacceleration in either directions shown by the arrows 106 and 107, thepiezoelectric element 101 is not subjected to tensile stresses.

Now without any loss of generality, let the shock loading experienced bythe sensor piezoelectric package 100, FIG. 36, be directed such that itcauses the piezoelectric package 100 to be accelerated (decelerated) inthe direction of the arrow 106 (107), thereby causing the mass elementto apply the compressive force to the piezoelectric element 102.

Also let the compressive shock loading profile that is experienced bythe piezoelectric element 102 be as shown in the (compressive) force vs.time plot of FIG. 37, i.e., be similar to the shock loading that can beexperienced by the munitions 40 of FIG. 22, to which the present shockloading detection and measuring sensor is attached. As a result, if theoutput of the piezoelectric element 102 is open and if there were nolosses associated with the piezoelectric element and if the object(munitions in this case) does not undergo any vibratory oscillations,then the profile of the charges generated by the piezoelectric elementwould be similar to that of the compressive force profile of FIG. 37(similar to the plot of FIG. 25B) (with the same timing cycle).

However, as was previously described, since a portion of the chargesgenerated by the piezoelectric element 102 during the shock loadingevent is either consumed by the connected sensor circuitry to bedescribed and or dissipated internally due to leakage and the like,therefore at the completion of the shock loading cycle, t₁ in FIG. 37,i.e., when the piezoelectric element has essentially returned to itsinitial strain state, there will be a negative charge (theaforementioned residual charge) left on the piezoelectric element (hereit is assumed that the compressive loading of the piezoelectric element102 due to the shock loading generates a positive charge on thepiezoelectric element 102). The purpose of the following embodiment isto rapidly eliminate the residual electrical charges so that theresulting sensory system would not erroneously detect tensile loading ofthe piezoelectric element, i.e., a “residual” shock loading in theopposite direction.

The schematic of the first embodiment of the piezoelectric basedmultiple shock loading detection and shock load profile measuring sensoris shown in FIG. 38. This circuitry uses the basic safety and all-firedetection circuitry shown in FIG. 13 and functions as was described forthe circuitry and is considered to be passive since it does not requireany external source of power or batteries or other similar sources ofchemical or externally charged power sources for its operation. Howeveras can be seen in the circuitry of FIG. 38 and to rapidly remove theaforementioned residual charges from the piezoelectric element(s)following the application of a shock loading event similar to that ofFIG. 37, a pair of serially connected diode D3 and resistor R4 areconnected to the terminals of the piezoelectric element as shown in FIG.38.

Then while the piezoelectric element is under compression as a result ofthe shock loading, the diode D3 is working at reversed voltage load sothere is no current passing through the pair, therefore the pair isinactive and does not change the characteristics of the impact sensingcircuitry. It is noted that the piezoelectric element is considered tobe designed to provide a positive voltage as a result of the compressiveloading. Then as the shock loading cycle ends, i.e., at or close to thetime t₁ in FIG. 37, the aforementioned residual negative chargesremaining on the piezoelectric element is allowed to pass through thediode D3 and will then pass through the resistor R4 and are dissipated.In general, the resistance of the resistor R4 is selected consideringthe capacitance of the piezoelectric element such that their timeconstant is close to the shock loading duration to effectively removethe residue energy. In the extreme case, the resistance of R4 can beessentially zero so that the accumulated negative charge is directlyreleased, i.e., the piezoelectric element may be shorted to dischargethe aforementioned residual negative charge.

It will be appreciated by those skilled in the art, that with theaddition of the diode D3 and relatively low resistance resistor R4 asshown in FIG. 38 to the basic safety and all-fire detection circuitry ofFIG. 13, the rectifying diode D1 may then be removed since there will beminimal negative voltage that would be required to be rectified by thediode D1.

As was previously indicated, the second component of “residual energy”imparted to the present piezoelectric based shock loading sensorysystems following a shock loading event is in the form of mechanicalvibration energy due to the structural flexibility of the variouscomponents of the sensory system, including the structural flexibilityof the sensor piezoelectric element(s) itself. The purpose of thefollowing (second) embodiment of the multiple shock loading sensorysystem is to rapidly dissipate this residual energy so that the shockloading event can be measured accurately and that at the end of eachshock loading cycle, the output level of the sensory system (effectivelysensory noise level) is reduced enough to allow for the detection andprecision measurement of the profile of the next shock loading event.

A schematic of the second embodiment of the piezoelectric based multipleshock loading detection and shock load profile measuring sensor is shownin FIG. 39. This circuitry uses the basic safety and all-fire detectioncircuitry shown in FIG. 13 and functions as was described for thecircuitry and is considered to be passive since it does not require anyexternal source of power or batteries or other similar sources ofchemical or externally charged power sources for its operation.

It will however be appreciated by those skilled in the art that thedeveloped circuitry for dissipating this component of the mechanicalresidual (vibrational) energy must function without significantlyaffecting the shock loading level profile and duration information. Itis however noted that when the sensory system is designed properly, theperiod of the (residual) vibrational energy, i.e., the period(s) naturalmode(s) of vibration of the sensory system, is designed to besignificantly higher than the duration of the shock loading pulse (t₁ inFIG. 37). Thus, by adding the pair of capacitor C2 and resistor R4 ortheir equivalent to the basic safety and all-fire detection circuitryshown in FIG. 13 as shown in FIG. 39 and by proper selection of thevalues of the capacitor C2 and the resistor R4, the high frequencycomponent of the piezoelectric output voltage, i.e., the aforementioned(high frequency) mechanical residual (vibrational) energy, isdissipated. It is noted that since the energy dissipated in the resistorR4 is to the second order of such current, the energy dissipated by theaddition of the present capacitor C2 and resistor R4 is very sensitiveto the signal (piezoelectric output) frequency. Therefore the capacitorC2 and the resistor R4 can be readily selected to effectively remove thevibration residue energy without changing the piezoelectric elementoutput due to the shock loading in terms of its level, profile, andduration.

In certain applications, the present piezoelectric based multiple shockloading detection and shock load profile measuring sensor is mounted ona platform which vibrates in one or more dominant modes of vibrationthat would thereby cause the sensor piezoelectric element to generate anunwanted output in addition to the shock loading profile to be measuredby the sensor as was previously described. In such cases, it is highlydesirable to significantly reduce the level of such sensor outputs. Ingeneral, the frequencies of such dominant modes of platform vibration(in most systems only one or at most two such modes of vibration aresignificant) are known or can be readily either calculated orexperimentally measured using well known analytical (usually usingFinite Element Methods) or experimental (using calibrated hammerimpacts) techniques. Therefore, by providing the means of dissipatingoutput (output energy) from the piezoelectric element within a frequencyrange (window) that includes one or all of the dominant modes ofplatform vibration without affecting the piezoelectric element outputdue to the shock loading in terms of its level, profile, and duration.Thereby the performance of the present piezoelectric based multipleshock loading detection and shock load profile measuring sensor issignificantly improved.

A third embodiment of the piezoelectric based multiple shock loadingdetection and shock load profile measuring sensor is intended todissipate the piezoelectric element output energy in a relatively smallfrequency range (window) for the purpose of significantly reducing thesensor output caused by the dominant natural mode(s) of vibration of theplatform to which the present sensor is attached as was described above.

The schematic of this third embodiment of the piezoelectric basedmultiple shock loading detection and shock load profile measuring sensoris shown in FIG. 40. This circuitry uses the basic safety and all-firedetection circuitry shown in FIG. 13 and functions as was described forthe circuitry and is considered to be passive since it does not requireany external source of power or batteries or other similar sources ofchemical or externally charged power sources for its operation.

In the embodiment of FIG. 40, to significantly dissipate thepiezoelectric element output energy in a relatively small frequencyrange (window) corresponding to the dominant mode(s) of vibrations ofthe platform to which the present sensor is attached, a seriallyconnected RLC circuitry (resistor R4, inductor L1 and capacitor C2) ortheir equivalent is added to the basic safety circuitry of FIG. 13. Thecapacitor C2, resistor R4 and inductor L1 construct an energydissipating circuitry. The capacitor C2 passes more current for highfrequency signal while the inductor passes more current for lowfrequency signal, so when they are serially connected, the current fromthe signal (i.e., output of the sensor piezoelectric element) with onlya range of frequency mostly passes to the sensor circuitry (through thediode D1), and the energy generated by the piezoelectric element due tothe platform vibration (at the aforementioned frequency(ies) of thedominant mode(s) of the platform vibration) is mostly dissipated withoutaffecting the piezoelectric element output due to the shock loading interms of its level, profile, and duration. Thereby the performance ofthe present piezoelectric based multiple shock loading detection andshock load profile measuring sensor is significantly improved.

In a fourth embodiment of the piezoelectric based multiple shock loadingdetection and shock load profile measuring sensor shown generally in theschematic of FIG. 41, a “control circuitry” is provided to dissipateresidual energy of the sensory system (mostly due to vibrationalexcitation) at the completion of each shock loading cycle (t₁ in FIG.37). The indicated “control circuitry” (examples of which to bedescribed below) is intended to monitor each shock loading profile todetect the end of its cycle (t₁ in FIG. 37), and when it is reached, toclose the switch K1, causing the electrical energy (charges) in thepiezoelectric element and those generated due to the vibration of theplatform to which the present sensory system is attached to bedissipated by the resistor R4. The resistance of the resistor R4 shouldbe selected to achieve relatively fast dissipation to minimize thesensor output before the expected occurrence of the next shock loadingevent. The switch K1 is then preferably opened as soon as the output ofthe piezoelectric element has dropped below a prescribed level.

The “control circuitry” component and the switch K1 shown in thecircuitry of FIG. 41 may be implemented in many different ways and usingmany different components. The method and circuitry presented in theschematic of FIG. 42 is intended to represent one such implementationand is not intended to exclude other implementations. In thisimplementation, the “control circuitry” is designed as shown in FIG. 42,with an N-Channel Mosfet M1 being used to function as the switch K1(FIG. 41), which is used to close the piezoelectric and resistor R4energy dissipation loop when a control voltage is applied on the gatepin of M1 when the “control circuitry” detects the end of a shockloading event. The control voltage is provided from the AND logic gateunit U2, which becomes high when the level from the buffer U1A is lowand the level from the buffer U2A is high. The buffers U1A and U2Aamplify input signal and output them at logic level. U1A takes thesafety output signal as input, outputs high level during a shock loadingevent. U2A takes input from an impact “history-keeping” signal to bedescribed later, which is generated from the diode D3, capacitor C2, andresistor R5, and outputs high level during a shock loading event. Theimpact history-keeping signal resets itself after a certain amount oftime, which is selected to be less than the minimum amount of timebetween two shock loading events. Therefore, to output control levelfrom the AND gate, two conditions must be true: the shock loading eventhas ended and the history shows that a shock loading event has occurredat a certain earlier time. When these two conditions are achieved, theMosfet M1 is enabled and energy dissipation begins via the passingcurrent through the resistor R4.

In the “control circuitry” component of the embodiment of FIG. 42, the“history-keeping” signal is the voltage on the capacitor C2. During ashock loading event, the voltage on the capacitor C2 will follow thesignal output voltage from safety circuitry signal (the node between theresistors R2 and R3, FIG. 42). Then when the shock loading ends and thesafety circuit output signal drops back to zero (in practice below aprescribed threshold), the diode D3 will prevent the capacitor C2 fromdischarging back, therefore the impact history information is preserved.In this circuitry, the resistor R5 provides a discharge loop for thecapacitor C2 and is used to reset the impact history recording. Thereset time determined by the loop RC (R5 and C2) time constant and isset considering the shock loading event durations and time intervals.

It is noted that the energy dissipation loop (containing the resistorR4) does not only discharge the residue energy from the piezoelectricelement, but also acts to counter the noise due to the structuralvibration of the platform to which the sensor is attached. As a result,the level of noise transmitted to the output circuitry is significantlyreduced. Then after the energy dissipation loop (containing the resistorR4) is disconnected (by the opening of the switch K1 in FIG. 41 andMosfet M1 in FIG. 42) by the aforementioned resetting of the switchingaction, the piezoelectric element generated noise signal should berelatively low; the energy stored in the capacitor C1 would beessentially zero and the sensor would be ready to detect and measure theprofile of the next shock loading event as was previously described.

In another implementation of the general embodiment of FIG. 41, a“control circuitry” is used to drive a power source V1 as shown in theschematic of FIG. 43 to effectively remove any one of the aforementionedtypes of the residue energy stored on or generated by the sensorpiezoelectric element. Such “control circuitry” retrieves vibrationsignal from the output of the piezoelectric element, and would generatean output feedback signal to drive the power source V1 to counter(eliminate) the residue energy. Such a power source may be, but is notlimited to, a voltage source, a current source or a charge source, andmay be connected to the output of piezoelectric element in series or inparallel, and may be coupled with an inductor or capacitors, and thelike, as is well known in the art.

In several of the above embodiments, methods were used to minimize theoutput of the sensor piezoelectric element due to high frequencyvibration of the platform to which the present sensor is attached. Inthe following embodiments, methods are provided that can be used inaddition to the aforementioned methods to significantly reduce the levelof high frequency vibrations that are transmitted from the platform tothe piezoelectric element of the present sensor. It will be appreciatedby those skilled in the art that by high frequency vibrations of theplatform to which the present sensor is attached, we refer to thosefrequencies with periods that are significantly smaller than theduration of the shock loading events to be measured. The high frequencyvibration is generally due to the structural vibration and so-calledringing (stress wave induced) reaction of the object such as munitionsto which the present sensory system is attached. The disclosed methodsand devices include those that are fully passive, i.e., do not requireexternal sources of electrical energy, as well as those that are active,i.e., utilize externally provided electrical energy.

In one such embodiment, the previously described embodiments areattached to the platform that is subjected to shock loading with anintermediate vibration isolation element, such as a resilient layer withproper flexibility and damping characteristics, to isolate the sensorfrom the aforementioned unwanted relatively high frequency vibration ofthe platform, for example as shown schematically in FIG. 44, forattaching the packaged piezoelectric element of the shock loadingdetection and measurement 100 of FIG. 36 to the platform 150 which is tobe subjected to multiple shock loading events. Methods to design suchvibration isolation elements and the materials appropriate for suchpurposes are well known in the art.

In the schematic of FIG. 44, the packaged piezoelectric element of theshock loading detection and measurement 100 of FIG. 36 is shown to beattached to the platform 150 which is to be subjected to multiple shockloading events with an intermediate vibration isolation material layer151. The vibration isolation layer element may be a sheet of resilientand high damping material or consist of several elements and/ormaterials which are designed to absorb and/or divert high frequencyplatform vibration, thereby isolating the sensor piezoelectric package100 from such platform vibrations. The base 152 of the package 100 maybe attached by fasteners (not shown) to the structure of the platform150 with provided vibration isolating resilient washers to prevent thetransmission of the platform vibration to the packaged element 100 andthereby the piezoelectric element of the multiple shock loading eventmeasurement sensor. The methods and devices for the design of suchvibration isolation devices and proper methods for their attachment tothe intended objects are well known in the art and will not be describedin detail here.

In a fourth embodiment of the piezoelectric based multiple shock loadingdetection and shock load profile measuring sensor shown generally in theschematic of FIG. 41, a “control circuitry” is provided to dissipateresidual energy of the sensory system (mostly due to vibrationalexcitation) as the completion of each shock loading cycle (t₁ in FIG.37).

In the general piezoelectric based multiple shock loading detection andshock load profile measuring sensor embodiment of FIG. 41 and itsimplementation example shown in FIG. 42, a passive method was presentedfor dissipating the energy remaining in the sensory system, mainly itspiezoelectric element and its related mechanical elements (for examplesee the elements in the piezoelectric packaging of FIG. 36) after thecompletion of the shock loading event or the aforementioned highfrequency energy being transmitted to the system from the platform towhich it is attached. The level of the high frequency energy beingtransmitted from the platform is significantly reduced by theintroduction of the passive isolation element such as the element 151shown in FIG. 44 as was previously described. However, if the level ofsuch transmitted high frequency energy is still excessive and/or if itdesired to more rapidly dissipate the aforementioned remaining(mechanical and/or electrical) energy at the completion of the shockloading event, then one may use the electrical energy generated by atleast one additional piezoelectric element that is positioned in seriesor in parallel with the sensor piezoelectric element to rapidlyeliminate the remaining or platform transmitted energies. It isappreciated by those skilled in the art that for the case of the (mostlyvibrational) energy being transmitted from the platform to thepiezoelectric element of the sensors, the added piezoelectric element(s)are in fast providing an active means of isolating the piezoelectricelement of the sensor from the platform to which it is attached, i.e., atask similar to that of the high frequency vibration isolation element151.

An example of such an implementation of the above method with oneserially added piezoelectric element is shown schematically in FIG. 45.In the schematic of FIG. 45, the packaged piezoelectric element of theshock loading detection and measurement 100 of FIG. 36 is shown to beattached to the platform 153 which is to be subjected to multiple shockloading events (the intermediate vibration isolation material layer 151shown in FIG. 44 may also be utilized but is not shown for the sake ofclarity). As can be seen in FIG. 45, an additional piezoelectric element154 is positioned between the sensor piezoelectric element 155 and thebase 156 of the piezoelectric packaging 101. The added seriallypositioned piezoelectric element 154 is to function to actively isolatethe sensor piezoelectric element 155 from the vibration of the platform153 and to dissipate the mechanical and electrical energy of the sensorysystem, primarily those of the piezoelectric packaged sensor component,once a shock loading event has ended and from high frequency vibrations(as was previously defined to mean those vibrations with periods thatare significantly smaller than the duration of the shock loading events)of the platform 153 during the shock loading event.

The schematic of a typical circuitry for actively driving theaforementioned added at least one piezoelectric element (element 154 inFIG. 45) is shown in FIG. 46. In the circuitry of FIG. 46, the platformvibration induced output of the added at least one “vibration isolatingpiezoelectric element” (element 154 in FIG. 45) is input to theindicated “control circuitry” element, which based on the output of theelement 154, and the current state of the sensor piezoelectric element(element 155 in FIG. 45) would apply an appropriate signal (voltage) tothe sensor piezoelectric element as well as the at least one “vibrationisolating piezoelectric element” to minimize the transmission of theplatform vibration to the sensor piezoelectric element at the completionof a shock loading event. The indicated battery is used to power theoperation of the “control circuitry” and drive the added at least onepiezoelectric element(s). During the shock loading, the “controlcircuitry” would similarly prevent the aforementioned high frequencyvibration to be transmitted to the sensor piezoelectric element. It willbe appreciated by those skilled in the art that to this end, theinformation as to the detected start and ending of each shock loadingevent is transmitted (not shown in FIG. 46) to the “control circuitry”of FIG. 46. The “control circuitry” would similarly dissipate (damp out)any residual vibration of the sensory elements (100 in FIG. 45) at theend of each shock loading event.

The various designs for the construction of the “control circuitry” ofFIG. 46 and their operation for the aforementioned vibration isolationand vibration damping purposes are well known in the art.

In the circuitry of FIG. 46, a battery is shown to be used to power theoperation of the “control circuitry” and drive the added at least onepiezoelectric element(s). It is, however, appreciated by those skilledin the art that the electrical energy generated by the added at leastone piezoelectric element(s) and to a degree, the piezoelectric elementof the sensor may also be harvested as was described in the previousembodiments (FIGS. 24-35) and used to directly power the circuitry ofFIG. 46 or supplement the power provided by the indicated circuitrybattery.

Consider the embodiment of the programmable safety and all-firedetection circuitry of FIG. 13. When the piezoelectric element of thecircuitry of FIG. 13 or the device using this circuitry, such as theembodiments of FIGS. 14-21, which may be as shown in FIG. 47, issubjected to an acceleration pulse, such as an acceleration in thedirection of the arrow 75 as shown in FIG. 47, the piezoelectric elementwould generate an open-circuit charge profile such as one of the twoshown in FIG. 48. As was previously described, the programmable safetyand all-fire detection circuitry of FIG. 13 is designed to be capable ofdifferentiating prescribed acceleration pulse events as described by aminimum acceleration pulse magnitude and a minimum of its duration (theso-called all-fire events for the case of gun-fired munitions andmortars) from other acceleration events that may occur duringmanufacture, assembly, handling, transport, accidental drops, etc. Suchevent is hereinafter also referred to as the “prescribed accelerationpulse event”.

The piezoelectric electrical energy generator 70 shown in FIG. 47 isusually constructed with a stack type piezoelectric element 71, inpresent self-powered circuitry or devices to generate electrical energywhen the device is subjected to shock loading, for example due to anacceleration pulse, such as one in the direction of the arrow 75. In theconfiguration shown in FIG. 47, the piezoelectric electrical energy(charge) generator 70 is shown as being fixedly attached to a basestructure 73, which is considered to be subjected at a certain point intime to an acceleration pulse in the direction of the arrow 75. Arelatively rigid mass 72 may also be required to react to theacceleration in the direction of the arrow 75 and apply a resultingcompressive force to the piezoelectric element 71. Then as a result ofthe compressive force and the internal normal compressive pressuregenerated in the piezoelectric element 71 due to its own mass as aresult of the said acceleration pulse, the piezoelectric element 71 isstrained (deformed) axially, and thereby would generate electricalcharges at its electrodes as is well known in the art. The leads 76,properly connected to the electrodes of the piezoelectric element 71,would make the generated charges available for connection to theprogrammable safety and all-fire detection circuitry of FIG. 47.

As was previously described, to detect the occurrence of a prescribedacceleration pulse event, the profile of the charge voltage generated bythe piezoelectric element of the programmable safety and all-firedetection circuitry of FIG. 13 or one of the aforementioned devicesusing this circuitry must satisfy the acceleration event minimummagnitude (threshold) and its minimum duration conditions. As was alsopreviously described, in the circuitry of FIG. 13 (alone or in a deviceusing this circuitry such as the embodiments of FIGS. 14-21) theacceleration pulse magnitude and duration thresholds are determined fromthe voltage of the capacitor C1, which is proportional to the magnitudeof the acceleration pulse experienced by the piezoelectric element. Theprescribed acceleration pulse magnitude and duration thresholds are setby proper selection of the resistance of the resistor R3 and thecapacitance of the capacitor C1 as is also previously described.

It will be appreciated by those skilled in the art that under relativelylow acceleration levels, such as those experienced during transportationinduced vibration, the voltage across the piezoelectric element is lowerthan the Z1 Zener diode voltage and since the diode D2 also blocks thecurrent flow into the capacitor C1, the capacitor C1 stays discharged.The Zener diode Z1 is generally used to set a minimum voltage thresholdlevel for blocking charging of the capacitor C1 by charges generated bythe piezoelectric element in response to low acceleration levels such asthose due to transportation induced accelerations. At such lowacceleration levels, no current will pass through the resistor R1 tocharge the capacitor C1. In general, the capacitance of the capacitor C1is selected to be very low and the resistance of the resistor R1 isselected to be high so that a very small portion of the electricalenergy generated by the piezoelectric element is consumed by the Z1, R1and C1 circuit.

In the programmable safety and all-fire detection circuitry of FIG. 13,the resistance of the resistor R1 is preferably kept unchanged and theresistance of the resistors R2 and R3 and the capacitance of thecapacitor C1 are appropriately selected to set the desiredaforementioned acceleration pulse magnitude and duration thresholds forthe circuit alone or as it may be integrated in other devices, such asthe embodiments of FIGS. 14-21 or the like. Then if the voltage of thecharges generated by the piezoelectric element passes the Z1 Zener diodevoltage, the reverse biased Z1 diode passes current to the capacitor C1,and the capacitor begins to be charged. If the acceleration pulseamplitude passes the prescribed threshold level and lasts longer thanthe prescribed duration threshold, the voltage of the capacitor C1 andthereby the OUTPUT voltage reach their prescribed threshold, indicatingthat the occurrence of the prescribed acceleration pulse event (all-firecondition for the case of gun-fire munitions or a prescribed impactcondition).

It will be, however, appreciated by those skilled in the art that whenthe programmable safety and all-fire detection circuitry of FIG. 13(alone or as it may be integrated in other devices, such as theembodiments of FIGS. 14-21 or the like) experiences an accelerationpulse, if the amplitude of the acceleration pulse is significantlyhigher than the aforementioned prescribed threshold level (the so-calledall-fire setback acceleration level for the case of gun-fired munitionsand mortars), then the higher voltage of the charges generated by thepiezoelectric element would charge the capacitor C1 to the prescribedvoltage threshold level a significant amount of time before theaforementioned acceleration pulse duration threshold has elapsed (i.e.,before the so-called all-fire event for the case of gun-fired munitionsand mortars is to be indicated). In some applications in whichaccidental acceleration amplitude levels could be significantly higherthan the prescribed acceleration pulse magnitude threshold and that theacceleration pulse threshold is relatively short, this shortcoming ofthe aforementioned embodiments may become unacceptable.

The “prescribed acceleration pulse event” detector embodiment 80 of FIG.49, which is obtained by the indicated modification of the programmablesafety and all-fire detection circuitry of FIG. 13, is configured toeliminate the aforementioned shortcoming of the embodiment itself and asintegrated in other devices, such as the embodiments of FIGS. 14-21 orthe like. The embodiment 80 of FIG. 49 is provided with the means oflimiting the voltage applied to the capacitor C1, FIG. 13, to apredetermined voltage level as described below. As a result, no matterhow high a voltage is generated by the device piezoelectric element,i.e., no matter how high above the prescribed threshold the magnitude ofthe acceleration pulse that is experienced by the device reaches, theduration of the pulse is detected based on the predeterminedacceleration pulse magnitude. As a result, the pulse duration of theacceleration pulse that is to be detected by the embodiment 80 of FIG.49 or a device using this embodiment becomes independent of how muchhigher the peak acceleration pulse magnitude may reach. The embodiment80 of FIG. 49 or any other device using this embodiment (such as theembodiments of FIGS. 14-21 or the like) would therefore become capableof differentiating a prescribed acceleration pulse event as described bya prescribed acceleration pulse magnitude threshold and a minimum of itsduration (the so-called all-fire event for the case of gun-firedmunitions and mortars), no matter how high magnitude accidental(no-fire) acceleration pulses could be experienced by the device.

The “prescribed acceleration pulse event” detector circuitry of theembodiment 80 of FIG. 49 is obtained by the addition of the Zener diodeZ2 or the like to the programmable safety and all-fire detectioncircuitry of FIG. 13. The resistor R6 is also added to ensure properoperation of the Zener diode Z2. In the embodiment 80 of FIG. 49 thediode D1 is also removed to allow free discharge from the storagecapacitor C1 for charges generated by single or multiple pulses withlower than the prescribed threshold magnitude for lower than thresholdduration, such as those due to accidental drops or transportationvibration. The “prescribed acceleration pulse event” detector circuitryof the embodiment 80 of FIG. 49 is configured to function similar tothat of the embodiment of FIG. 13, except that the charging voltageapplied to the capacitor C1 and used to detect the aforementionedprescribed acceleration pulse magnitude threshold is limited at a presetlevel. As a result, the duration of the acceleration pulse forindicating the prescribed acceleration pulse event (such as the all-firecondition for munitions due to setback acceleration or due to an impactevent) is measured at the prescribed acceleration pulse magnitudethreshold level, even if the magnitude of the acceleration pulse issignificantly higher than the acceleration pulse magnitude threshold.

The design and operation of the embodiment 80 of FIG. 49 will bedescribed by its application to construct a programmable electricallyinitiated inertial igniter of the type shown in FIG. 15 but with thecapability of differentiating a prescribed acceleration pulse event asdescribed by a prescribed acceleration pulse magnitude threshold and aminimum of its duration (the so-called all-fire event for the case ofgun-fired munitions and mortars), no matter how high magnitudeaccidental (no-fire) acceleration pulses could be experienced by thedevice. The resulting programmable electrically initiated inertialigniter is shown as the embodiment 85 in FIG. 50. The embodiment 80 ofFIG. 49 may be used similarly in the construction of any other devicerequiring such acceleration pulse event detection capability, such asthose of the embodiments of FIGS. 14-21.

The programmable electrically initiated inertial igniter embodiment 85shown in FIG. 50 is constructed similarly to the embodiment of FIG. 15by the addition of the indicated “Output Voltage Threshold Detection andSwitching Element” of FIG. 15 to the “prescribed acceleration pulseevent” detector circuitry of the embodiment 80 of FIG. 49. The resistorR5 is also added to the “Output Voltage Threshold Detection andSwitching Element” component of the embodiment 85 to improve thelatching operation of the Q1 and Q2 pair.

In this embodiment, the safety and all-fire detection circuitryembodiment 80 of FIG. 49 is provided with the “output voltage thresholddetection and switching element” as shown in FIG. 50. By appropriatelyselecting the component parameters of the circuitry, when the voltage atthe OUTPUT of the safety and all-fire detection circuitry reaches theprescribed all-fire threshold as was described for the safety andall-fire detection circuitry embodiment 80 of FIG. 49, the N-MOS(indicated as Q1 in FIG. 50) is switched on. During this switching-onprocess, the voltage on the resistor R4 increases and produces a currentIBE on NPN transistor (indicated as Q3 in FIG. 50) in the direction ofthe arrow at B. The NPN transistor Q3 amplifies the current andintroduces current IBE on PNP transistor Q2, while the PNP transistor Q2amplifies the current and sends it back to the NPN transistor Q3. Thispositive feedback configuration of the two transistors Q2 and Q3 atcertain point saturates the two transistors, making them act as a“switch” that has been closed between the points 81 and 82, FIG. 50,thereby allowing the charges generated by the piezoelectric element tobe discharged through the indicated “bridge wire” to the ground (GND).The very low resistance initiator bridge wire is then heated by thepassing current, which would then ignite the provided (usually primary)pyrotechnic material.

As was described for the safety and all-fire detection circuitryembodiment 80 of FIG. 49, the piezoelectric transducer produces a charge(at certain voltage) profile when subjected to an acceleration pulseprofile. For the N-MOS (indicated as Q1 in FIG. 50) to be switched onand initiate the process of passing the piezoelectric element chargesthrough the bridge wire as was described above, the voltage at theOUTPUT of the safety and all-fire detection circuitry must reach thegate threshold voltage (V_(gth)) of the N-MOS (indicated as Q1 in FIG.50). For the voltage at the OUTPUT to reach the gate threshold voltage(V_(gth)) of the N-MOS, the piezoelectric generated charge (voltage)profile satisfies the aforementioned two conditions. Firstly, themagnitude of the piezoelectric generated voltage profile must reach aprescribed voltage threshold (hereinafter indicated as the voltageV_(th)), and secondly if the magnitude of the piezoelectric generatedvoltage profile remains above the prescribed voltage threshold V_(th) aprescribed amount of time, hereinafter indicated as the (time) durationt_(d).

The programmable electrically initiated inertial igniter embodiment 85shown in FIG. 50 is configured with the components of its safety andall-fire detection circuitry, i.e., the embodiment 80 of FIG. 49 portionof its circuitry, such that when both of the above two (prescribedvoltage magnitude threshold as well as duration) conditions aresatisfied.

As an example, in a programmable electrically initiated inertial igniterembodiment 85 shown in FIG. 50, with a safety and all-fire detectioncircuitry embodiment of FIG. 13, i.e., without the capacitor C1 chargingvoltage limiting Zener diode Z2, the voltage at the junction 83, FIG.50, as the piezoelectric element of the device was subjected to animpact pulse corresponding to a prescribed acceleration pulse is shownin the measured voltage plot of FIG. 51 (as indicated by the voltageV_(C1) profile). The same circuit with the added Zener diode Z2 with a10 V limiting capability would however limit the voltage V_(C1) to 10volts as shown in the measured voltage plot of FIG. 52. It will beappreciated by those skilled in the art that since the voltage V_(C1) isthe voltage at which the input acceleration pulse threshold indicatingcapacitor C1 is charged, therefore with the added Zener diode Z2,irrespective on how high the piezoelectric charge generated voltagereaches, the amount of time that it takes for the OUTPUT voltage toreach the prescribed threshold, i.e., the time duration t_(d) is notaffected. Thus, the prescribed OUTPUT threshold is reached once thepiezoelectric voltage (i.e., the magnitude of the acceleration pulse)reaches its prescribed threshold and also stays above the said thresholdat least the amount of time corresponding to the prescribed durationt_(d).

In certain applications, the prescribed acceleration pulse event to bedetected by the safety and all-fire detection circuitry embodiment 80 ofFIG. 49 is desired to be used for arming (enabling) a device orcircuitry. In such applications, the function of the arming mechanism isto ensure that the device cannot be activated/operated unless the devicehas been armed, i.e., has experienced the prescribed acceleration pulseevent to be detected. Such applications include munitions in whichcertain devices need to be armed post firing or certain objects in whichcertain onboard devices need to be armed post a prescribed impactinduced acceleration pulse profile. All other acceleration events, suchas those with larger than the prescribed minimum acceleration pulsemagnitude threshold but significantly shorter duration or significantlysmaller than the prescribed acceleration pulse magnitude threshold andlong in duration (the so-called no-fire conditions in munitions), shouldnot arm (enable) the device. The events (no-fire conditions inmunitions) may occur during manufacture, assembly, handling, transport,accidental drops, or other similar accidental events.

The prescribed acceleration pulse event detection capability of thesafety and all-fire detection circuitry embodiment 80 of FIG. 49 for theconstruction of arming (enabling) functionality for various devices andcircuits will be described below using an example of its application toa laser activated initiation device embodiment 90 shown in FIG. 53. Inthe laser activated initiation device embodiment 90 of FIG. 53, once theprescribed acceleration pulse event (all-fire event in munitions) hasbeen detected by the detection of the prescribed acceleration pulsemagnitude threshold and its duration threshold, the MOSFET Q1 isactivated, then the remaining charges that are generated by thepiezoelectric element are routed through the fuse (bridge wire) F1 shownin FIG. 53. In this circuit, the resistance of the resistor R7 isselected to be high and the resistance of the fuse F1 is selected to bevery low (such as on the order of 1-3 Ohms), therefore almost all thegenerated current by the activation of the MOSFET Q1 is passed throughthe fuse F1 and causes it burn, thereby opening the indicated circuitparallel to the resistor R7.

It will be appreciated by those skilled in the art that in the laseractivated initiation device circuit of FIG. 53, the MOSFET Q4 acts as anormally open switch. If the MOSFET Q1 is not activated, i.e., if thelaser activated initiation device embodiment 90 has not detected theprescribed acceleration pulse event, since the fuse F1 is intact, thedrain and source pins of the MOSFET Q4 are shorted by the fuse F1,causing the MOSFET Q4 to remain in cut off mode, i.e., act as an openswitch. During this state of the MOSFET Q4, any current that may begenerated by the photovoltaic cell cannot activate the MOSFET Q1. Withthe intact fuse F1, any current generated by the photovoltaic cellpasses almost entirely through the resistor R8 since the resistance ofthe resistor R7 is very high and that of the fuse F1 is very low, ineffect the fuse F1 is shorting the resistor R7. Therefore, thenegligible amount of current passing through the fuse F1 cannot burn itsfilament and therefore the MOSFET Q1 still acts as an open switch. As aresult, any current generated by the photovoltaic cell would not passthrough the “initiation bridge wire”, FIG. 53. That is, as long as thelaser activated initiation device embodiment 90 of FIG. 53 is not armed(enabled) by the device detection of the prescribed acceleration pulseevent (the all-fire condition in munitions) and consequent burning ofthe fuse F1 filament, the activated initiation device 90 is in itsdisarmed (not enabled) state.

As an example, consider the case in which the photovoltaic cell isproducing a voltage of 5 V. If the resistance of the resistors R7 and R8are 5 MΩ and the resistance of the fuse F1 is 3Ω, then the currentpassing through the fuse F1 will be around 1 μA, which the fuse F1 isdesigned to readily withstand.

It will be appreciated by those skilled in the art that once theaforementioned prescribed acceleration pulse event (all-fire event inmunitions) has been detected by the detection of the prescribedacceleration pulse magnitude threshold and its duration threshold, theMOSFET Q1 is activated, and the remaining charges that are generated bythe piezoelectric element is routed through the fuse (bridge wire) F1shown in FIG. 53 as was described for the embodiment of FIG. 50 and aswas previously described will burn the filament of the fuse F1. At thispoint, laser activated initiation device embodiment 90 shown in FIG. 53is armed (enabled) and the drain and source pins of transistor Q4 are nolonger shorted by the fuse F1. Now when current is generated by thephotovoltaic cell by the user laser beam (light source), voltage dropacross the resistors R4 and R5 causes the MOSFET Q4 to be activated.Once the MOSFET Q4 is activated, the previously open “switch” Q4 becomesclosed. Thus, since the resistances of the resistors R7 and R8 are high,almost all the current generated by the photovoltaic cell is passedthrough the low resistance “initiation bridge wire” if it were connecteddirectly to the photovoltaic cell through the MOSFET Q4, i.e., withoutthe intermediate components shown in the circuit of FIG. 53.

In the laser activated initiation device embodiment 90 of FIG. 53, thephotovoltaic cell may be any photosensitive cell, such as a photodiodeor a photovoltaic cell or an array of such cells, such as thephotovoltaic cell with part number CPC1822 by IXYS Corporation. Thelight source for the photovoltaic cell may be a high-power LED or alaser diode such as part number SLD3234VF by Sony Corporation. Ingeneral, when higher currents are needed, more than one photovoltaiccell and light source may be used, and the photovoltaic cells areconnected together in parallel configuration.

In the laser activated initiation device embodiment 90 of FIG. 53, theinitiation bridge wire must be heated rapidly to minimize cooling and toachieve high enough temperatures for reliable ignition of pyrotechnicmaterials at even low environmental temperatures. In this laseractivated initiation device embodiment, a sufficient amount ofelectrical energy is first generated by the photovoltaic cell and storedin a storage capacitor C2, and is then suddenly passed through the verylow resistance (such as 1-3 Ohm or less) initiation bridge wire at highcurrent levels. The initiation bridge wire is thereby heated during avery short period of time, and considering the natural relatively longtime constant of heat conduction into the surrounding regions, thetemperature of the initiation filament is rapidly raised to ignite thesurrounding pyrotechnic material. In addition, an LED light shown inFIG. 53 can also be provided to alert the user of the initiation bridgewire heating.

It will be appreciated by those skilled in the art that the level ofcurrent that the electrical energy storage capacitor C2 shown in FIG. 53can discharge through the initiation bridge wire is proportional to itsvoltage and that photovoltaic cells can only generate voltages of a fewvolts unless several of them are used simultaneously and with strongenough light sources. The circuitry choice, however, can use acircuitry, such as a voltage booster to step up the photovoltaicgenerated voltage to charge the electrical energy storage capacitor C2for discharge at a high enough voltage, i.e., by passing a high enoughcurrent through the initiation bridge wire for its rapid heating totemperatures needed to ignite the initiator pyrotechnic material.

In the laser activated initiation device embodiment 90 of FIG. 53, theenergy storage capacitor C2 is the intended high voltage electricalenergy storage capacitor that is to be charged by the electrical energygenerating photovoltaic cell through the aforementioned voltage boosterafter the laser activated initiation device has been armed (enabled),i.e., after the MOSFET Q4 is activated following detection of theprescribed acceleration pulse and burning of the fuse F1.

To achieve the higher required voltage across the energy storagecapacitor C2 from the low voltages generated by the photovoltaic cellsof the device, a voltage booster circuit comprising of a transistor Q5and coupled inductors N2 and N1 (N1>N2) provides a practical solution asshown in FIG. 53. These coupled inductors can be provided by atransformer T1 shown in the circuit of FIG. 53. The circuitconfiguration of the two inductors N2 and N1 and the transistor Q5 forman oscillator which progressively charges the capacitor C2.

The operation of the voltage booster circuit of the laser activatedinitiation device embodiment 90 is based on positive feedback providedby the proportional relationship between the transistor Q5 base currenti1 and the collector current i2, FIG. 53. At the beginning of thecharging cycle, that is when the photovoltaic cell is illuminated, thebase current i1 and therefore the collector current i2 are zero andbegin to increase in response to the photovoltaic cell generatedvoltage. The collector current i2 increases at a rate which may be afactor of 200 times greater than the base current i1, due to the currentgain of the transistor. In this manner, increasing collector currentcauses increase in the collector-emitter voltage, which results in anincrease in the base current, which in turn increases the collectorcurrent, resulting in positive feedback. The process continues until thecollector current reaches its maximum value, at which point thetransistor Q5 is in its saturated state, and the voltage across theinductors goes to zero, and as a result the base current i1 goes tozero, and the transistor Q5 switches off, resulting in zero collectorcurrent i2. The charged inductor N1 now reverses polarity and the energyfrom N1 is dumped into the capacitor C1 as the diode D3 which waspreviously reverse biased now becomes forward biased. Once thetransistor Q5 base current i1 goes to zero, the cycle repeats asphotovoltaic cell is still illuminated. The voltage across the capacitorC2 builds up in this step-wise manner until the voltage across thecapacitor C2 reaches a level above the breakdown voltage of the Zenerdiode Z3, at which point the transistor Q6 switches into the ON stateallowing current to flow through the initiation bridge wire. The LEDlight (if provided) also comes on, alerting the user of the initiationbridge wire heating. The initiation bridge wire is thereby heated veryrapidly, allowing it to initiate (ignite) the provided pyrotechnicmaterial. The current flow through the initiation bridge wire will go tozero either if the initiation bridge wire is burned or the voltageacross the capacitor C2 falls below the Zener diode breakdown voltage.

A second embodiment 95 of the laser activated initiation device of thepresent invention is shown in FIG. 54. This embodiment is identical tothe embodiment 90 of FIG. 53, except that a timing circuit is alsoprovided that would delay the discharge of the electrical energy fromthe energy storage capacitor C2 through the initiation bridge wire oncethe voltage of the capacitor has reached its prescribed level. In themodified circuit of FIG. 54, once the voltage across the capacitor C2 islarger than the Zener voltage of Z3, the transistor Q6 is activated andcurrent begins to flow into the capacitor C3 through the resistor R11.The transistor Q7 is a MOSFET which acts as a switch. The transistor Q7is initially open and it is closed when the capacitor C3 is charged to avoltage equal or larger than transistor Q7 gate threshold voltage. Thecapacitance of C3 is significantly smaller than that of the capacitanceof the capacitor C2 so that minimal electrical energy is discharged intothe capacitor C3 from the capacitor C2. The transistor Q7, resistor R11and the capacitor C3 together form a timer. The amount of time that ittakes for the voltage across the capacitor C3 to reach the transistor Q7gate threshold voltage level is determined by the time constant of theresistor R11 and capacitor C3. By properly selecting the resistance ofthe resistor R11 and the capacitance of the capacitor C3, the amount oftime that it takes for the transistor Q7 to be activated followingactivation of the transistor Q6 can be set to the desired value.

Once the capacitor C3 is charged to transistor Q7 gate thresholdvoltage, the transistor Q7 is activated. At this point if the circuit isnot provided with a switch SW2 or if the circuit is provided with aswitch SW2 but the switch is in its closed state, then current flowsfrom the capacitor C2 through the initiation bridge wire. The initiationbridge wire is thereby heated very rapidly, allowing it to initiate(ignite) the provided pyrotechnic material.

The laser activated initiation device embodiment 95 shown in FIG. 54 canbe provided with a normally open switch and an LED light as can be seenin FIG. 54. Then as the electrical energy storage capacitor C2 ischarged to the expected voltage, the LED light goes on, indicating thatthe capacitor C2 is charged with enough electrical energy. Then at anydesired time the user can close the switch SW2, starting the timerformed by the resistor R11 and the capacitor C3. Then after theresulting time delay, the transistor Q7 is activated as was previouslydescribed, thereby discharging the capacitor C2 through the initiationbridge wire. The initiation bridge wire is thereby heated very rapidly,allowing it to initiate (ignite) the provided pyrotechnic material.

It is appreciated by those skilled in the art that different types ofphotovoltaic cells are currently available and that any one of suchcells, which could be eliminated by an appropriate light source such asa high-power LED or a diode laser, or the like may be used in thedisclosed embodiments of FIGS. 53-54. Similarly, photodiodes or othersimilar cells, well known in the art, may be used in place of theindicated photovoltaic cells.

The prescribed acceleration pulse event detection capability of thesafety and all-fire detection circuitry embodiment 80 of FIG. 49 for theconstruction of arming (enabling) functionality for various devices andcircuits was described using an example of its application to a laseractivated initiation device embodiment 90 shown in FIG. 53. In the laseractivated initiation device embodiment 90 of FIG. 53, once theprescribed acceleration pulse event (all-fire event in munitions) hasbeen detected by the detection of the prescribed acceleration pulsemagnitude threshold and its duration threshold, the MOSFET Q1 isactivated, then the remaining charges that are generated by thepiezoelectric element are routed through the fuse (bridge wire) F1 shownin FIG. 53. In this circuit, the resistance of the resistor R7 isselected to be high and the resistance of the fuse F1 is selected to bevery low (such as on the order of 1-3 Ohms), therefore almost all thegenerated current by the activation of the MOSFET Q1 is passed throughthe fuse F1 and causes it burn, thereby opening the indicated circuitparallel to the resistor R7.

As was described for the laser activated initiation device circuit ofFIG. 53, the MOSFET Q4 acts as a normally open switch. If the MOSFET Q1is not activated, i.e., if the laser activated initiation deviceembodiment 90 has not detected the prescribed acceleration pulse event,since the fuse F1 is intact, the drain and source pins of the MOSFET Q4are shorted by the fuse F1, causing the MOSFET Q4 to remain in cut offmode, i.e., act as an open switch. During this state of the MOSFET Q4,any current that may be generated by the photovoltaic cell cannotactivate (close) the MOSFET Q4. With the intact fuse F1, any currentgenerated by the photovoltaic cell passes almost entirely through theresistor R8 since the resistance of the resistor R7 is very high andthat of the fuse F1 is very low, in effect the fuse F1 is shorting theresistor R7. Therefore, the negligible amount of current passing throughthe fuse F1 cannot burn its filament and therefore the MOSFET Q4 stillacts as an open switch. As a result, any current generated by thephotovoltaic cell would not pass through the “initiation bridge wire”,FIG. 53. That is, as long as the laser activated initiation deviceembodiment 90 of FIG. 53 is not armed (enabled) by the device detectionof the prescribed acceleration pulse event (the all-fire condition inmunitions) by the burning of the fuse F1 filament, the initiation device90 is in its disarmed (not enabled) state.

Then as was described for the embodiment 90 of FIG. 53, once theaforementioned prescribed acceleration pulse event (all-fire event inmunitions) has been detected by the detection of the prescribedacceleration pulse magnitude threshold and its duration threshold, theMOSFET Q1 is activated, and the remaining charges that are generated bythe piezoelectric element is routed through the fuse (bridge wire) F1shown in FIG. 53. At this point, laser activated initiation deviceembodiment 90 shown in FIG. 53 is armed (enabled) and the drain andsource pins of MOSFET Q4 are no longer shorted by the fuse F1. Now whencurrent is generated by the photovoltaic cell by the user laser beam(light source), voltage drop across the resistors R4 and R5 causes theMOSFET Q4 to be activated. Once the MOSFET Q4 is activated, thepreviously open “switch” Q4 becomes closed. Thus, since the resistancesof the resistors R7 and R8 are high, almost all the current generated bythe photovoltaic cell is passed through the low resistance “initiationbridge wire” if it were connected directly to the photovoltaic cellthrough the MOSFET Q4, i.e., without the intermediate components shownin the circuit of FIG. 53.

In the laser activated initiation devices such as the embodiment 90 ofFIG. 53, the initiation bridge wire must be heated rapidly to minimizecooling and to achieve high enough temperatures for reliable ignition ofpyrotechnic materials at even low environmental temperatures. For thisreason and was previously described, a sufficient amount of electricalenergy is first generated by the photovoltaic cell and stored in astorage capacitor C2, and is then suddenly passed through the very lowresistance (such as 1-3 Ohm or less) initiation bridge wire at highcurrent levels. The initiation bridge wire is thereby heated during avery short period of time, and considering the natural relatively longtime-constant of heat conduction into the surrounding regions, thetemperature of the initiation filament is rapidly raised to ignite thesurrounding pyrotechnic material. In addition, an LED light shown inFIG. 53 can also be provided to alert the user of the initiation bridgewire heating.

It is appreciated that once the laser activated initiation deviceembodiments 90 and 95 of FIGS. 53 and 54, respectively, are armed(enabled) as was previously described by the burning of the fuse (bridgewire) F1, then a laser source may be used at any time after the saidinitiation device enabling event to generate electrical energy throughthe photovoltaic cell and consequently pass a high enough currentthrough the initiation bride wire to ignite its surrounding pyrotechnicmaterial.

It is, however, appreciated by those skilled in the art that in manyapplications, once the laser activated initiation device embodiments 90and 95 of FIGS. 53 and 54, respectively, are armed (enabled) as waspreviously described by the burning of the fuse (bridge wire) F1, thenonly within a limited amount of time, which may span from a few secondsto minutes or hours, or at most one or two days, the laser source isused to generate electrical energy through the photovoltaic cell andconsequently pass a high enough current through the initiation bridewire to ignite its surrounding pyrotechnic material. The following(third and fourth) embodiments 100 and 105 of the present inventionshown in FIGS. 55 and 56, respectively, are intended for used in thesaid applications.

It is also appreciated by those skilled in the art that the embodiments90 and 95 of FIGS. 53 and 54, respectively, may also be used in theabove applications. However, as is shown below, the embodiments 100 and105 of the present invention shown in FIGS. 55 and 56, respectively,have the following and in some cases highly significant advantages,which may even prohibit their use in certain n applications, over thesaid embodiments 90 and 95. These advantages include firstly the factthat the design laser activated initiation device is simplified by theelimination of the fuse F1, which is generally more costly and bulkythan the replacing capacitor C4 (FIGS. 55 and 56). The resistors R7 andR8 are also eliminated. Secondly and more importantly, the laseractivated initiation device embodiments 90 and 95 of FIGS. 53 and 54,respectively, are for one-time use only, i.e., once the fuse F1 has beenburned, the device stays armed and can only be used for the process ofigniting the provided pyrotechnic material via the initiation bridgewire. However, the laser activated initiation device embodiments 100 and105 of the present invention shown in FIGS. 55 and 56, respectively, aredis-armed (disabled) after a certain (prescribed) length of time and canno longer initiate the said pyrotechnic material with the use of thelaser source. This characteristic of the laser activated initiationdevice embodiments 100 and 105 provides them with the safety featurethat is required in many applications.

The aforementioned third embodiment 100 of the laser activatedinitiation device of the present invention is shown in FIG. 55. Allcomponents of the embodiment 100 are identical to those of the laseractivated initiation device embodiment 90 of FIG. 53, except that thefuse F1 is replaced by the capacitor C4 and that the resistors R7 and R8are removed. In the resulting embodiment 100, FIG. 55, once theprescribed acceleration pulse event (all-fire event in munitions) hasbeen detected by the detection of the prescribed acceleration pulsemagnitude threshold and its duration threshold, the MOSFET Q1 isactivated, and the remaining charges that are generated by thepiezoelectric element are routed to the capacitor C4 for storage.

As was described for the laser activated initiation device circuit ofFIG. 53, the MOSFET Q4 acts as a normally open switch. If the MOSFET Q1is not activated, i.e., if the laser activated initiation deviceembodiment 90 has not detected the prescribed acceleration pulse event,the capacitor C4 is not charged and therefore no external voltage isapplied across the drain and source pins of the MOSFET Q4, causing theMOSFET Q4 to remain in cut off mode, i.e., act as an open switch. Inthis state of the MOSFET Q4 the laser activated initiation deviceembodiment 100 of FIG. 55 is not armed (is disabled), and as waspreviously described, any voltage that may be generated by thephotovoltaic cell cannot activate the MOSFET Q4, i.e., to make it act asa closed switch. With the MOSFET Q4 acting as an open switch, anyvoltage generated by the photovoltaic cell cannot produce a current tocharge the energy storage capacitor C2 for powering the initiationbridge wire circuit. The laser activated initiation device embodiment100 of FIG. 55 is therefore disarmed, i.e., not enabled.

Now once the prescribed acceleration pulse event (all-fire event inmunitions) is detected by the laser activated initiation deviceembodiment 100 of FIG. 55 by the detection of the prescribedacceleration pulse magnitude threshold and its duration threshold, theMOSFET Q1 is activated, and the remaining charges that are generated bythe piezoelectric element are routed to the capacitor C4 for storage.The resulting voltage that the charged capacitor C4 applies across thedrain and source pins of the MOSFET Q4 activates the MOSFET Q4 andcauses it to act as a closed switch, thereby causing the laser activatedinitiation device embodiment 100 of FIG. 55 to be armed (enabled).

It is appreciated by those skilled in the art that the MOSFET Q4 staysactivated (i.e., acts as a closed switch) as long as the voltageprovided by the capacitor C4 is above its activation voltage.

It is also appreciated by those skilled in the art that by using a lowleakage capacitor C4 and low leakage MOSFET Q4 (e.g., a low capacitancecapacitor C4 with a capacitance of 500 nano-F that is charged by arelatively small piezoelectric element to 10 Volts and a MOSFET Q4 ofmodel ZVN3310FTA from Diode Inc.) can be shown to keep the laseractivated initiation device embodiment 100 of FIG. 55 in its armed(enabled) state for over 6-7 days.

It is also appreciated by those skilled in the art that by providing aresistor (not shown) with an appropriate resistance level in series withthe capacitor C4, the duration of time that the laser activatedinitiation device embodiment 100 of FIG. 55 stays armed (enabled) can beset to a prescribed level.

A forth embodiment 105 of the laser activated initiation device of thepresent invention is shown in FIG. 56. This embodiment is identical tothe embodiment 100 of FIG. 55, except that a timing circuit is alsoprovided that would delay the discharge of the electrical energy fromthe energy storage capacitor C2 through the initiation bridge wire oncethe voltage of the said capacitor has reached its prescribed level. Thearming (enabling) circuit modifications of the embodiment 105 isidentical to the modifications previously described for the embodiment95 of FIG. 54.

In the modified circuit of FIG. 56, as was previously described for theembodiment 95 of FIG. 54, once the voltage across the energy storagecapacitor C2 is larger than the Zener voltage of Z3, the transistor Q6is activated and current begins to flow into the capacitor C3 throughthe resistor R11. The LED is also lit and indicate that the energystorage capacitor is charged to the prescribed level. The transistor Q7is a MOSFET which acts as a switch. The transistor Q7 is initially openand it is closed when the capacitor C3 is charged to a voltage equal orlarger than transistor Q7 gate threshold voltage. The capacitance of C3is significantly smaller than that of the capacitance of the capacitorC2 so that minimal electrical energy is discharged into the capacitor C3from the capacitor C2. The transistor Q7, resistor R11 and the capacitorC3 together form a timer. The amount of time that it takes for thevoltage across the capacitor C3 to reach the transistor Q7 gatethreshold voltage level is determined by the time constant of theresistor R11 and capacitor C3. By properly selecting the resistance ofthe resistor R11 and the capacitance of the capacitor C3, the amount oftime that it takes for the transistor Q7 to be activated followingactivation of the transistor Q6 can be set to the desired value. It isappreciated that the transistor Q6 acts as a closed switch when thevoltage across C2 is higher than the sum of the Zener voltage of Z3, theforward voltage for the Light Emitting Diode (LED) and the minimumBase-Emitter voltage required for enabling the Q6. Otherwise, Q6 act asan open switch.

Once the capacitor C3 is charged to the transistor Q7 gate thresholdvoltage, the transistor Q7 is activated. At this point if the circuit isnot provided with a switch SW2 or if the circuit is provided with aswitch SW2 but the switch is in its closed state, then current wouldflow from the energy storage capacitor C2 through the initiation bridgewire. The initiation bridge wire is thereby heated very rapidly,allowing it to initiate (ignite) the provided pyrotechnic material. Ifthe switch SW2 is open, then the current is allowed to flow from theenergy storage capacitor C2 through the initiation bridge wire andignite the provided pyrotechnic material once the user closes the switchSW2.

It will be appreciated by those skilled in the art that the level ofcurrent with which an electrical energy storage capacitor can dischargeits energy through an initiation bridge wire, for example, the level ofcurrent with which the energy storage capacitor C2 of the embodiment 90or 100 of FIGS. 53 and 55, respectively, is proportional to its voltage.As a result, higher the said capacitor voltage, faster the rise in theinitiation bridge wire temperature and faster its adjacent pyrotechnicmaterial is ignited. This is the reason for the provision of thepreviously described voltage boosters for the circuit of the embodiments90 and 95 of FIGS. 53 and 54, respectively, and the embodiments 100 and105 of FIGS. 55 and 56, respectively. It has been shown that with suchhigh voltage (of the order of 30-40 Volts) charged capacitors,pyrotechnic materials may be reliably ignited in a fraction ofmilliseconds.

It is also appreciated by those skilled in the art that in manyapplications, the aforementioned very fast pyrotechnic initiation maynot be required. In such applications, voltage generated by the laserpowering of the photovoltaic cell may be used to directly charge theenergy storage capacitor C2 as shown in the fifth embodiment 110 of thepresent invention of FIG. 57. The circuit of the embodiment 110 of FIG.57 is identical to that of the embodiment 100 of FIG. 55, except thatits voltage booster components have been removed. The laser activatedinitiation device embodiment 110 of FIG. 57 also functions as wasdescribed for the case of the embodiment 100 of FIG. 55.

It is also appreciated by those skilled in the art that photovoltaiccells may be connected in series to provide higher capacitor chargingvoltages to the energy storage capacitor C2 in the embodiment 100 ofFIG. 57. In fact, such serially connected cells are currently availablecommercially. The user therefore has the option to use such seriallyconnected photovoltaic cell assemblies to achieve higher energy storagecapacitor C2 voltage, thereby faster pyrotechnic material ignition withthe laser activated initiation device embodiment 110 of FIG. 57. Anothermethod of achieving faster pyrotechnic material ignition (not shown) isto connect several energy storage capacitors C2 initially in paralleland charging them to close to maximum photovoltaic cell providedvoltage, and the connecting them in series to achieve a higher totaldischarge voltage through the initiation bridge wire. Such switchingcircuit options using electronic switches are well known in the art.

A sixth embodiment 115 of the laser activated initiation device of thepresent invention is shown in FIG. 58. This embodiment is identical tothe embodiment 105 of FIG. 57, except that a timing circuit is alsoprovided that would delay the discharge of the electrical energy fromthe energy storage capacitor C2 through the initiation bridge wire oncethe voltage of the said capacitor has reached its prescribed level. Thearming (enabling) circuit modifications of the embodiment 115 isidentical to the modifications previously described for the embodiment105 of FIG. 56.

Once the laser activated initiation device embodiment 115 of FIG. 58 isarmed (enabled) as was described for the embodiment 105 of FIG. 56, theuser can begin the pyrotechnic initiation process. Similar to theprocess described for the said embodiment 105, the photovoltaic cell isenergized by a laser source to start generating electrical energy forstorage in the energy storage capacitor C2. Once the voltage across theenergy storage capacitor C2 is larger than the Zener voltage of Z3, thetransistor Q6 is activated and current begins to flow into the capacitorC3 through the resistor R11. The LED is also lit and indicate that theenergy storage capacitor is charged to the prescribed level. Similarly,the transistor Q7 is a MOSFET and acts as a switch. The transistor Q7 isinitially open and is closed when the capacitor C3 is charged to avoltage equal or larger than transistor Q7 gate threshold voltage. Thecapacitance of the capacitor C3 is significantly lower than that of thecapacitance of the capacitor C2 so that minimal electrical energy isdischarged into the capacitor C3 from the capacitor C2. The transistorQ7, resistor R11 and the capacitor C3 together form a timer. The amountof time that it takes for the voltage across the capacitor C3 to reachthe transistor Q7 gate threshold voltage level is determined by the timeconstant of the resistor R11 and capacitor C3 and by properly selectingthe resistance of the resistor R11 and the capacitance of the capacitorC3, the amount of time that it takes for the transistor Q7 to beactivated following activation of the transistor Q6 can be set to thedesired value. Once the capacitor C3 is charged to the transistor Q7gate threshold voltage, the transistor Q7 is activated. At this point ifthe circuit is not provided with a switch SW2 or if the circuit isprovided with a switch SW2 but the switch is in its closed state, thencurrent would flow from the energy storage capacitor C2 through theinitiation bridge wire. The initiation bridge wire is thereby heatedrapidly, allowing it to initiate (ignite) the provided pyrotechnicmaterial. If the switch SW2 is open, then the current is allowed to flowfrom the energy storage capacitor C2 through the initiation bridge wireand ignite the provided pyrotechnic material once the user closes theswitch SW2.

It is appreciated by those skilled in the art that in the embodiment 110of FIG. 57, current begins to flow from the energy storage capacitor C2through the initiation bridge wire once the transistor Q6 has beenactivated as the voltage across the energy storage capacitor C2 is largeenough to activate the transistor Q6, i.e., the sum of the Zener voltageof Z3, the forward voltage of LED and the minimum base-emitter voltagerequired voltage for Q6. The voltage across the capacitor C2 will thenbegin to drop until it reaches below the said Q6 activation level,causing the transistor Q6 to act as an open switch. At this point, thecapacitor C2 still holds a portion of its initial electrical energy,i.e., all the electrical energy stored in the energy storage capacitorC2 is not discharged through the initiation bridge wire. Similarly, forthe case of the embodiment 115 of FIG. 58, the capacitor C2 still holdsa portion of its initial electrical energy following the circuit timeractivation of the transistor Q7 and closing of the switch SW2 todischarge electrical energy stored in the energy storage capacitor C2through the initiation bridge wire.

The following embodiments 120 and 125 of FIGS. 59 and 60, respectively,of the present invention are intended to eliminate the above shortcomingand allow the electrical energy stored in the energy storage capacitorC2 in the embodiments of FIGS. 53-58 to fully discharge through theinitiation bridge wire. The provided embodiments, however, require morecomponents and can therefore be considered to be more complex.

The seventh embodiment 120 of the laser activated initiation device ofthe present invention is shown in FIG. 59. This embodiment is identicalto the embodiment 110 of FIG. 57, except that the LED, resistor andZener diode Z3 and the transistor Q6 are replaced by the switchingcircuit with the latching capability described below. The embodiment 110may also be provided with the indicated “Status LED” circuit shown inFIG. 59.

In the embodiment 120, the device is armed (enabled) as was describedfor the embodiments 100, 105, 110 and 115 of FIGS. 55-58, respectively.Then once it is armed (enabled), the user can illuminate thephotovoltaic cell be an appropriate laser source, thereby generating avoltage to charge the energy storage capacitor C2. It is appreciatedthat the energy storage capacitor C2 can only be charged to the opencircuit voltage of the photovoltaic cell, less the minimum forwardvoltage of diode D3.

The laser activated initiation device embodiment 120 of FIG. 59 may beprovided with the switch SW1, which when open would prevent the flow ofcurrent from the energy storage capacitor C2 into the initiation bridgewire circuit. If the embodiment 120 is provided with the Status LEDcircuit shown in FIG. 59, the said circuit described below is powered bythe energy storage capacitor C2 regardless the status of the switch SW1.

A status LED (Light Emitting Diode) circuit is included in theembodiment. The “Status LED” circuit detects the voltage level acrossthe energy storage capacitor and LED1 is illuminated only when thevoltage across C2 is beyond a certain threshold. The threshold value canbe changed by varying the ratio between resistors R6 and R7. Voltageacross R7 is used to enable the N-MOSFET Q5. The MOSFET Q5 together withresistor R8 form an inverted logic driver for the gate terminal of theP-MOSFET Q6. Transistors Q5 and Q6 form a two-stage MOSFET circuit. Whenvoltage across R7 is above a certain value, current flows through the“Status LED” in series with the current limiting resistor R9 and theLED1 is illuminated.

Once the LED1 is illuminated, the used is made aware that the energystorage capacitor C2 is charged to the required voltage threshold. Atthis point, the user can close the switch SW1 at the desired point oftime, thereby allowing the current to flow from the energy storagecapacitor C2 to the initiation bridge wire portion of the circuit.

The resistors R12 and R13 form a voltage divide. When the voltage acrossenergy storage capacitor C2 reaches a prescribed threshold level, thevoltage across R13 is designed to reach the gate threshold voltage ofthe MOSFET Q7. The MOSFET Q7 is then activated to drive a P-MOSFET Q8with the pull up resistor R11. The combination of the diode D4 andcapacitor C5 are used to maintain the voltage at the gate input of Q7 sothat Q8 acts as a latching switch. The transistor Q8 is chosen tosatisfy the voltage and current requirement of the bridge wire. When Q8is activated, the entire electrical energy stored in the energy storagecapacitor C2 is thereby directed to flow through the initiation bridgewire, and thereby ignite the provided pyrotechnic material.

A eighth embodiment 125 of the laser activated initiation device of thepresent invention is shown in FIG. 60. This embodiment is identical tothe embodiment 120 of FIG. 59, except that a timing circuit is alsoprovided that would delay the discharge of the electrical energy fromthe energy storage capacitor C2 through the initiation bridge wire oncethe voltage of the said capacitor has reached its prescribed level andthe switch SW1 has been closed.

In the laser activated initiation device embodiment 125 of FIG. 60, oncethe device is armed (enabled) as was described for the embodiment 105 ofFIG. 56 and the energy storage capacitor C2 is charged to the thresholdvoltage level, at which time the LED1 light is illuminated (whenpresent), then the user can close the switch SW1 at a desired time andthereby start the process of device pyrotechnic material initiation.Similar to the process described for the said embodiment 105 of FIG. 56,the energy storage capacitor C2 is charged by the voltage generated bythe photovoltaic cell as it is energized by a laser source.

Once the user closes the switch SW1 to initiate the process of ignitingthe device pyrotechnic material, the capacitor C5 is charged through thediode D4. At the same time, the capacitor C6, which is selected to havea capacitance that is much smaller than that of the capacitor C6, beginsto be charged, but at significantly lower rate though the diode D4 andthe resistor R10, which is selected to have a relatively largeresistance. It is appreciated that in this circuit the resistor R10 andthe capacitor C6 together form an RC timer and provide the means ofdelaying pyrotechnic material initiation for a desired length of time.When the voltage across the capacitor C6 reaches the gate thresholdvoltage of the MOSFET Q7, the MOSFET Q7 is activated and subsequentlyenable the MOSFET Q8 to act as a closed switch. The MOSFET Q8 will thenallow the current to flow from the energy storage capacitor C2 throughthe initiation bridge wire. In this circuit, the capacitor C5 allows theMOSFET Q8 to be enabled for an extended period of time to allow most ofthe stored electrical energy in the capacitor C2 to be passed throughthe initiation bridge wire. The initiation bridge wire is thereby heatedrapidly, allowing it to initiate (ignite) the provided pyrotechnicmaterial.

It is appreciated by those skilled in the art that the capacitance ofthe capacitor C5 should be larger than the capacitance of the capacitorC6 to ensure that gate threshold voltage of the MOSFET Q7 is maintained.The time delay for enabling the MOSFET Q8, i.e., for causing it to actas a closed switch, can be set by the proper selection of the resistanceof the resistor R10 and the capacitance of the capacitor C6. It is alsoappreciated that the resistor R11 is provided for the purpose of keepingthe MOSFET Q8 enabled as the electrical energy stored in the energystorage capacitor C2 is discharged through the initiation bridge wire.

It is appreciated by those skilled in the art that the latchingcapability of the embodiment 120 of FIG. 59 may also be incorporatedinto the laser activated initiation device embodiments 90, 95, 100 and105 of FIGS. 53, 54, 55 and 56, respectively. To this end, the LED,resistor and Zener diode Z3 and the transistor Q6 circuit of thesedevices are replaced by the switching circuit with the latchingcapability described for the embodiment 120 of FIG. 59. In addition, thesaid embodiments 90, 95, 100, 105 may also be similarly provided withthe indicated “Status LED” circuit of the embodiment 120 shown in FIG.59.

It is appreciated by those skilled in the art that the latchingcapability of the embodiment 125 of FIG. 60 and its capability todischarged essentially all the electrical energy that is stored in theenergy storage capacitor C2 through the initiation bridge wire may alsobe similarly incorporated into the laser activated initiation deviceembodiments 90, 95, 100 and 105 of FIGS. 53, 54, 55 and 56,respectively. To this end, the LED, resistor and Zener diode Z3 and thetransistor Q6 circuit of these devices are replaced by the switchingcircuit with the latching and electrical discharge capability describedfor the embodiment 125 of FIG. 60. In addition, the said embodiments 90,95, 100, 105 may also be similarly provided with the indicated “StatusLED” circuit of the embodiment 120 shown in FIG. 59.

While there has been shown and described what is considered to bepreferred embodiments of the invention, it will, of course, beunderstood that various modifications and changes in form or detailcould readily be made without departing from the spirit of theinvention. It is therefore intended that the invention be not limited tothe exact forms described and illustrated, but should be constructed tocover all modifications that may fall within the scope of the appendedclaims.

What is claimed is:
 1. A device responsive to an acceleration pulseevent, the device comprising: a piezoelectric device configured togenerate a voltage over a duration responsive to one or moreacceleration pulse events; a first electrical storage device configuredto receive a portion of the generated voltage to accumulate a firstcharge and configured to produce a detection signal in response to theaccumulated first charge indicating that the one or more accelerationpulse events met predetermined threshold magnitude and/or durationlimit(s); a second electrical storage device coupled to thepiezoelectric device and configured to accumulate a second charge fromthe piezoelectric device following production of the detection signal; abridge wire; a voltage and/or current source; and a switch that couplesor decouples the voltage and/or current source to the bridge wireresponsive to the accumulated second charge; wherein the voltage and/orcurrent source is a current source and the bridge wire is coupled to thecurrent source though a current amplifying circuit that amplifiescurrent produced by the current source.
 2. The device of claim 1,further comprising pyrotechnic material positioned in proximity to thebridge wire wherein the bridge wire is configured to ignite thepyrotechnic material in response to the switch coupling the voltageand/or current source to the bridge wire and the voltage and/or currentsource being activated.
 3. The device of claim 1, wherein the voltageand/or current source is a light activatable voltage and/or currentsource.
 4. The device of claim 3, wherein the light voltage and/orcurrent source is a laser activated voltage and/or current source. 5.The device of claim 1, wherein the voltage and/or current source is aphotovoltaic cell.
 6. The device of claim 1, wherein the voltage and/orcurrent source is a voltage source, the device further comprisingpyrotechnic material positioned in proximity to the bridge wire whereinthe bridge wire is configured to ignite the pyrotechnic material inresponse to the coupling of an output voltage from the voltage source tothe bridge wire.
 7. The device of claim 1, wherein the second storagedevice is a capacitor that is configured to maintain the second chargefor a predetermined period of time.
 8. The device of claim 1, whereinthe second storage device is a capacitor that is configured to maintainthe second charge for a programmable period of time.
 9. The device ofclaim 1, comprising a third energy storage device configured to becharged by the voltage and/or current source to a threshold voltage,whereinafter the charge from the third energy storage device is coupledto the bridge wire.
 10. The device of claim 9, further comprising alight configured to turn on when the third energy storage device reachesthe threshold voltage.
 11. The device of claim 1, further comprising avoltage delay circuit configured to delay providing a voltage resultingfrom the switch coupling the voltage and/or current source to the bridgewire for a predetermined period of time.
 12. The device of claim 11,further comprising a third energy storage device configured to becharged by the voltage and/or current source to a threshold voltage,whereinafter the voltage delay circuit is configured to delay providingthe threshold voltage from the third energy storage device to the bridgewire for a predetermined period of time.
 13. The device of claim 1,wherein the piezoelectric device is configured to be responsive to atleast one of setback acceleration and an impact event.
 14. The device ofclaim 13, wherein the piezoelectric device comprises a piezoelectricelement configured as a stack type piezoelectric element.
 15. The deviceof claim 13, wherein the piezoelectric device comprises a piezoelectricelement positioned between a rigid mass and a base structure.
 16. Thedevice of claim 1, wherein the voltage and/or current source comprises aplurality of voltage and/or current sources.
 17. The device of claim 1,comprising: a third energy storage device configured to be charged bythe voltage and/or current source to a threshold voltage, and a latchingswitch circuit coupled between the third energy storage device and thebridge wire.
 18. The device of claim 17, comprising a light configuredto turn on when the third energy storage device reaches the thresholdvoltage.
 19. The device of claim 1, comprising: a third energy storagedevice configured to be charged by the voltage and/or current source toa threshold voltage; a switch; and a delay circuit, wherein the switchis coupled between the delay circuit and the third energy storage deviceand the delay circuit is coupled between the switch and the bridge wire,wherein the delay circuit is configured to delay providing an outputresulting from coupling the threshold voltage to the bridge wire for apredetermined period of time after the switch is switched to a closedposition.
 20. The device of claim 19, comprising a light configured toturn on when the third energy storage device reaches the thresholdvoltage.
 21. A device responsive to an acceleration pulse event, thedevice comprising: a piezoelectric device configured to generate avoltage over a duration responsive to one or more acceleration pulseevents; a first electrical storage device configured to receive aportion of the generated voltage to accumulate a first charge andconfigured to produce a detection signal in response to the accumulatedfirst charge indicating that the one or more acceleration pulse eventsmet predetermined threshold magnitude and/or duration limit(s); a secondelectrical storage device coupled to the piezoelectric device andconfigured to accumulate a second charge from the piezoelectric devicefollowing production of the detection signal; a bridge wire; a voltageand/or current source; and a switch that couples or decouples thevoltage and/or current source to the bridge wire responsive to theaccumulated second charge; wherein the voltage and/or current source isa voltage source, the device further comprising pyrotechnic materialpositioned in proximity to the bridge wire wherein the bridge wire isconfigured to ignite the pyrotechnic material in response to thecoupling of an output voltage from the voltage source to the bridgewire; and the voltage and/or current source is a photovoltaic cell, thedevice further comprising a light source configured to couple light tothe photovoltaic cell.
 22. The device of claim 21, wherein the lightsource comprises a plurality of light sources configured to couple lightto the photovoltaic cell.
 23. A device responsive to an accelerationpulse event, the device comprising: a piezoelectric device configured togenerate a voltage over a duration responsive to one or moreacceleration pulse events; a first electrical storage device configuredto receive a portion of the generated voltage to accumulate a firstcharge and configured to produce a detection signal in response to theaccumulated first charge indicating that the one or more accelerationpulse events met predetermined threshold magnitude and/or durationlimit(s); a second electrical storage device coupled to thepiezoelectric device and configured to accumulate a second charge fromthe piezoelectric device following production of the detection signal; abridge wire; a voltage and/or current source; and a switch that couplesor decouples the voltage and/or current source to the bridge wireresponsive to the accumulated second charge; wherein the voltage and/orcurrent source is photovoltaic cell, the device further comprising avoltage booster circuit configured to boost an output voltage from thephotovoltaic cell that is provided to the bridge wire.
 24. A deviceresponsive to an acceleration pulse event, the device comprising: apiezoelectric device configured to generate a voltage over a durationresponsive to one or more acceleration pulse events; a first electricalstorage device configured to receive a portion of the generated voltageto accumulate a first charge and configured to produce a detectionsignal in response to the accumulated first charge indicating that theone or more acceleration pulse events met predetermined thresholdmagnitude and/or duration limit(s); a second electrical storage devicecoupled to the piezoelectric device and configured to accumulate asecond charge from the piezoelectric device following production of thedetection signal; a bridge wire; a voltage and/or current source; and aswitch that couples or decouples the voltage and/or current source tothe bridge wire responsive to the accumulated second charge; wherein thedevice is a programmable laser activated initiation device.
 25. A deviceresponsive to an acceleration pulse event, the device comprising: apiezoelectric device configured to generate a voltage over a durationresponsive to one or more acceleration pulse events; a first electricalstorage device configured to receive a portion of the generated voltageto accumulate a first charge and configured to produce a detectionsignal in response to the accumulated first charge indicating that theone or more acceleration pulse events met predetermined thresholdmagnitude and/or duration limit(s); a second electrical storage devicecoupled to the piezoelectric device and configured to accumulate asecond charge from the piezoelectric device following production of thedetection signal; a bridge wire; a voltage and/or current source; and aswitch that couples or decouples the voltage and/or current source tothe bridge wire responsive to the accumulated second charge; wherein thedevice is a portion of an all-fire detection circuit for a laseractivated initiation device.
 26. A device responsive to an accelerationpulse event, the device comprising: a piezoelectric device configured togenerate a voltage over a duration responsive to one or moreacceleration pulse events; a first electrical storage device configuredto receive a portion of the generated voltage to accumulate a firstcharge and configured to produce a detection signal in response to theaccumulated first charge indicating that the one or more accelerationpulse events met predetermined threshold magnitude and/or durationlimit(s); a second electrical storage device coupled to thepiezoelectric device and configured to accumulate a second charge fromthe piezoelectric device following production of the detection signal; abridge wire; a voltage and/or current source; and a switch that couplesor decouples the voltage and/or current source to the bridge wireresponsive to the accumulated second charge; wherein the detectionsignal is provided as an all-fire detection signal to a laser activatedinitiation device.
 27. A device responsive to an acceleration pulseevent, the device comprising: a piezoelectric device configured togenerate a voltage over a duration responsive to one or moreacceleration pulse events; a first electrical storage device configuredto receive a portion of the generated voltage to accumulate a firstcharge and configured to produce a detection signal in response to theaccumulated first charge indicating that the one or more accelerationpulse events met predetermined threshold magnitude and/or durationlimit(s); a second electrical storage device coupled to thepiezoelectric device and configured to accumulate a second charge fromthe piezoelectric device following production of the detection signal; abridge wire; a voltage and/or current source; a switch that couples ordecouples the voltage and/or current source to the bridge wireresponsive to the accumulated second charge; and a voltage delay circuitconfigured to delay providing a voltage resulting from the switchcoupling the voltage and/or current source to the bridge wire for apredetermined period of time; wherein the voltage delay circuit is afirst voltage delay circuit and the predetermined period of time is afirst predetermined period of time, the device comprising a secondvoltage delay circuit coupled between the first voltage delay circuitand the bridge wire, wherein the second voltage delay circuit isconfigured to delay providing a voltage resulting from the switchcoupling the voltage and/or current source to the bridge wire for asecond predetermined period of time following the first predeterminedperiod of time.